I've been trying to watch my anime (yea yea) and over the ensuing months these dad gum files are of such high quality that they're making my mac hiccup.

Especially the wmv's, although MKVs are just as notorious. I try using Flip4Mac but it's barely playable even with it. I have a 1.33 GHz PB G4 (latest Tiger update, latest QT update, etc), it's about three years old. Is my system basically a dinosaur now when it comes to these (virtually) HD-type formats? Any software help or hints would be very much appreciated!