From what I understand the 7500's can be
completely upgraded with decently fast
G4's and good video cards. I'm not sure how
they would run OSX...but with a fast
accelerator and video (along with drives/etc),
they should run nicely. If I recall, you can
upgrade the "backside" cahce that among other
things may help for better speed with OSX etc...
but I'm not sure on those details.