My Adium aliases are stored in ~/Library/Application Support/Adium/Users/<screen name>/BuddyList.plist.
By the way, I'm using Adium 1.5.1. Earlier versions may have a different preferences structure, in which case you might want to upgrade.
Are you sure you:
- Copied the entire directory tree over properly?
- Are using the same screen name on the old machine as on the new one?
Alex