unlike Windows7, OSX 10.6 is not backwards compatible with older machines. Going with a G5 means your OSX experience ends at 10.5. An old 1GHz Pentium 3 w/1GB RAM can run Win7 32bit albeit slowly, but it'll run. You will be limited to software that supports G5's, not that this is necessarily a bad thing as there's great software for G5's out there.