AmiMSN needs to be updated I think, I haven't been able to login for a while with it either.
SabreMSN is probably crashing because of the PNG images it uses and the avatars from other users are locking up your datatypes. You can either install the Picture.datatype from Picasso96 and newer PNG and JPEG datatypes, or you can use an image converter to change all the included images to IFF/ILBM. You should also increase the stack (in the Icon Information) to 1048576 or something really high and see if that helps.
