Yeah, I wouldn't really bother with aMSN......
Don't get me wrong, it works very well, and it does a great job mimicking the older MSN Messenger interface... but TCL/Tk ... have you ever seen it? It's uuuuugly! It won't look good or consistent with the rest of your interface... and as far as I know there's no easy way to change how it looks (think old 'Motify' look).
That is why I would strongly recommend an app that uses either Qt or GTK+. If you're a KDE lover, Kopete is an excellent multiprotocol MSN system, and KMess is a very good MSN client. If you're a GTK+ or GNOME fan, GAIM will be the best for you, although it doesn't support some MSN functions currently, such as file transfer (which afaik are supported in aMSN, Kopete and KMess).