Yeah, AFAIK both Classilla and iCab are a bit resource hungry, mostly in ram. (You do have a nice amount for a 8500 though.)

If you go into the forum User CP, Board Preferences, you can change the board style from "prosilver" (the default,) to "subsilver2" (a more HTML4 compliant theme.) Subsilver2 works well with IE5. (Not sure about IE4.5, should be fine.)

Nice conquest, I've always thought it'd be cool to have a TowerMac. (Older than my PowerMac G4 that is.)