QT works pretty much the same in any Mac, it's software after all. As far as I know all PBs run QT fine, and I have the 3ivx plugin for QT installed and watching AVIs on my PB (G3 500) just fine.
I like to have VLC installed as a backup though, as it comes in handy from time to time.
go to
www.versiontracker.com and in the search field type "divx" and you'll get various things that could help, for example Divx Doctor and such.