What is the most up to date variation of iTunes that will work on a PowerPC-based Mac?
The existing variation (iTunes 10) will certainly work on a PowerPC equipment yet it has some tiny constraints (largely it can not play High Definition video clip from the iTunes Store)
Mac computer system with an Intel, PowerPC G5 or G4 cpu
Intel, PowerPC G5 or 1.0 GHz PowerPC G4 or faster cpu is called for to play Standard Definition video clip from the iTunes Store
2.0 GHz Intel Core 2 Duo or faster cpu is called for to play HD video clip, an iTunes LP, or iTunes Extras from the iTunes Store
Mac OS X variation 10.5 or later on
Source (iTunes Download Page)