Forgotten Password

Also, Adium recommends searching through your keychain. Here are their instructions on that:

"Looking it up in Keychain Access

If you don't remember what service you use, you'll first need to open up the Accounts pane of Adium's Preferences, and then refer to the List of Services to determine the name of the service.
Keychain Access is located at /Applications/Utilities/Keychain Access.app.

1. Launch Keychain Access.
2. Scroll through to the list to the keychain items that start with “Adium”. Adium names its keychain items in the format “Adium.service-name.random-number”, so if you're looking for, say, an AIM account, it will be one of the “Adium.AIM.number” items. (There is no way to tell which account in Adium has which number in the Keychain. Sorry.)
3. Double-click on the keychain item.
4. Check the box labeled “Show password”.
5. Enter your Keychain password. This is probably the same password you use to log into Mac OS X.
6. Click Allow Once.
7. Select your password, copy it, and paste it into Adium's password field.
8. Quit Keychain Access.
9. Select some other text and copy it, to get your password off of the Clipboard. (You don't want to accidentally paste it into a message and send it!)

If you have multiple keychain items for the same service, you'll need to go through each one looking for the right password, assuming you didn't use the same password on all of them (and you shouldn't).
But wait—there's more!

If you use any other IM clients, such as the official client for your IM service, you should look through the Keychain for keychain items saved by those clients."

From the Adium web site