For those of you without a MobileMe account, this solution won’t work (which is another reason to consider getting this great service). For those of you with a MobileMe account, let’s proceed. I am going to assume that you have only a single-user MobileMe account. If you have a family account, then without any more help, this hint will work if you are also the administrator of the Time Capsule. In addition, I am assuming you have already set up your Mac to back up to your Time Capsule. This solution is for adding a remote backup function, not setting up your Mac to use Time Capsule.

Basics

You need a few things to start: Your MobileMe user name and password, an internet connection, and administrator access to your Time Capsule. If you’re the only person using all of these, you should be all set.

The first thing we need to do is make sure you have set up your MobileMe account on your Mac. If you already have done this and turned on Back To My Mac, skip down to “Getting the Password” For the rest of us, you can find the MobileMe preferences in your System Preferences (access those from the Dock, your Applications folder, or the Apple Menu). Note: If you’re still running a plain-vanilla version of 10.5 Leopard and have never used Software Update, your Mac may still list the MobileMe preference as .Mac. I highly recommend you run all of your software updates before proceeding.

Here’s what we’re looking for:

Once you click on the MobileMe preference, your account page will come up. If you have not entered your MobileMe user name and password, it will provide fields for you to do so. Once you enter this information and it is verified you should get a screen similar to this:

The key here is that the screen says you are signed into MobileMe. Once that’s the case, click on “Back to My Mac.” Once on this screen, you need to click on the “Start” button to turn on the service. Note: If you don’t want to use the Back to My Mac service, that’s ok. We only need the computer to connect to the MobileMe servers once to generate a password. Once Back To My Mac is running, you can feel free to shut it off.

Great! Now you can quit your System Preferences.

Getting the Password

Now that we’ve set up our MobileMe account and Back To My Mac, we need to get our Back To My Mac password. To do so, go to your Applications Folder. From there, open your Utilities folder. Finally, in the Utilities folder, open the program called “Keychain Access.”

In the upper left pane, click on the “System” keychain. Then, look for the key that is the kind called “Back to My Mac key.” You’ll probably only have one of these, and it take the form of username.members.mac.com or username.members.me.com, where username = your MobileMe user name. It looks like this:

Now, double click on that key, and a new window will open. At the bottom, click on the checkbox next to “Show password.” A new administrator verification window will pop up, and you need to enter your computer’s admin password in order to view your Back to Your Mac password. Once done, you should see something like this:

Finally, highlight the password and copy it into your clipboard. We will need this password in just a minute. (Alternately, you can copy and paste it into a sticky if you think you’re going to need to use the clipboard before we finish this set up.) Take note of whether your account says username.members.mac.com or username.members.me.com. It does matter, so write it down. If you’ve only added your account since .Mac switched to MobileMe, it’ll say me.com. If you’re an old .Mac user, it’ll probably say .mac.com. Now you can quit Keychain Access. (If the program asks you if you want to save changes, say no.)

Time Capsule Setup

The last big job we have is to make some changes to the Time Capsule setup. You’ll need to open your AirPort Utility, which is in the same folder as Keychain Access. Once you open the AirPort Utility, you should see your Time Capsule listed in the window, like this:

Obviously, my Time Capsule is called Satellite. Double click on your Time Capsule. You may then have to enter your Time Capsule’s password in order to configure your settings. Once that window opens, you’ll be on the Summary tab. Click on the “Time Capsule” tab, then click the Edit button, as shown here:

Once you click the Edit button, you should get a window like this:

Ok! This is where the meat of the project comes in:

• You will not have the “Use dynamic global hostname” checkbox checked, but we want to do so now.
• Make sure you have something filled in for “Local Hostname.” Anything is fine.
• Now, back on the “Hostname” line, we’re going to fill it in with a long string. The first word will be your local hostname. Since mine is Satellite, my first word is satellite. Then I put a period, followed by my MobileMe user name (in my photo, I just put the word “username.” You’ll replace it.). After that, you’ll put another period, followed by members.mac.com or members.me.com, depending on what your keychain indicated your account used.
• On the “User” line, this is again going to be your MobileMe user name, followed by a period, followed by members.mac.com or members.me.com (whichever is correct for your account).
• On the “Password” line, you DO NOT put your MobileMe password. Instead, you paste the password we copied from the System Keychain.
• Now, click Done, then click the Update button to have your Time Capsule save the settings and restart.

Are we done yet?

Maybe. Theoretically, we’re done! You should be able to leave your home, go to a coffee shop or anywhere else with a wireless network, and within a few minutes of getting online, your Mac should detect your Time Capsule. I have found that, in some cases, it doesn’t quite work perfectly until we try a couple of steps at least one time.

If you go to another wireless network and then check your Time Machine system preference, look to see whether your Time Capsule is recognized. If it is, then you should actually have a date and time listed next to the “Next Backup” line. If you do not, try this:

• Simply turn off Time Machine and turn it back on. Wait a minute, and see if this does not correct the problem.
• If it still does not, go to the finder, then click on the “Go” menu, followed by “Connect to Server.” For the address, type in that entire host name string. On my computer it was satellite.username.members.mac.com (where username was my username). Then click Connect. If you did not set up your Time Capsule with a password to connect, it should connect on its own. If you set up a simple password only for the device (rather than usernames and passwords), then when the username/password box pops up, your username will be “user” and your password will be whatever you set up on your Time Capsule. Finally, if you chose to use specific usernames and passwords for Time Capsule, enter your username and password. Once your Time Capsule appears under your Devices tab on your Finder window (or Desktop), you can eject the Time Capsule. NOW, go back to your Time Machine preference, turn Time Machine off and then back on and wait a minute to see if the problem has gone away.

These two steps above should only be needed in rare circumstances. For most people, everything should work without the extra steps. A few more notes:

• If you’re like me and are stuck with a crummy cable connection at home or remotely, your upload speed is probably not very good, and this will significantly impact how long your Time Machine backups take. In my experience, the “Preparing” step in the Time Machine takes 20-30 minutes remotely before you even get an indicator of how much data needs to be backed up. This isn’t a bug; this is simply what happens when you’re not on a local connection.
• Since backups take much longer, you might want to consider downloading a program that lets you schedule your backups rather than using the standard every-hour-when-my-machine-is-plugged-in setting. I recommend the wonderful and free Time Machine Editor.

Update: If, after trying all the steps below, your Time Capsule still does not appear in the Time Machine list of disks, open Terminal and type this command, press return, then reopen  System Preferences to look for the disk:

efaults write com.apple.systempreferences TMShowUnsupportedNetworkVolumes -bool yes

Did this work for you? Have a suggestion to improve this answer? Post your thoughts in the comments section!