IMAC -> iMac
MAC Pro -> Mac Pro
Mac ≠ MAC = media access control
That said, the new iMac will blow the doors off your G4. Go to an Apple Store and try it out. Regarding the glossy vs. matte screen issue, there have already been so many threads on it, just try a search and see what people wrote. And again, go check it out for yourself. Go to an Apple store. Check display angles, color accuracy, and glare for yourself.