Mac OS X 10.4.5 ("Tiger"). I have an iMac G5. It's definitely a lot better than a PC, it has built-in wireless LAN (AirPort), bluetooth, and speakers. It's also a monitor and computer in one box instead of a monitor plus a big box.\n\nG5's are definitely faster than Celeron 1.8 GHz machines, which I previously had. Since many of the computer manufacturers still sell Celerons as low-end computers, I just figured I would let you know.