I didn't try to install wpmu on my powermac, and I won't.
about the mulitple domains thing.
as far as I can see from the db-contents it seems that blogs are bounded to a specific domain. so test.AAAA.com should be different from test.BBBB.com
BUT currently the blogs are created with tables like $prefix_$username_... which is quite bad because this doesn't allow to have test.AAA.com and test.BBB.com because both would create the same tables.
blog-aliases would be a solution for that problem, or at least separating the table creation for a blog from the username.
To add another domain take a look into the database, specific the 'site' table, and play around with adding a new entry. don't forget to add a default blog for the new domain too.