I have a 7500 with a G4-1ghz upgrade and it's a beast. I also have a beige G3 with a G4-500 and a 7600 with a G3-400 and though none of them matches my Powermac G4, they are all brutes running period software and games.

Installing OS X to these is possible but may be challenging if you're not comfortable playing around with the open firmware. The whole 5400-6400 5500-6500 family were probably the worst Powermacs because of the memory architecture and the fact that you could only upgrade the CPU through the L2 slot. You only get 128megs with a x500 and I think 136 with a x400 which means you can't run OS X with them. The CPU also precludes OS X because OS X doesn't see the CPU upgrade, only the onboard 603, and won't run. I'd try to find a G4 or early G5 Powermac if you really need a replacement. With sound and video so I can play Ambrosia games like Barrack, Apeiron, Mars Rising.Would a P4 2.8ghz be beefy enough to replicate G3/400 performance?Edit 7/7/11: So to summarise what seems to be around for Windows based on replies received and then browsing wikipedia:VMac emulates early 68k Macs and runs up to 7.5.5Basilisk II emulates later 68k Macs and can run up to OS8.1Sheepshaver emulates early PowerPC Macs and can run OS's 7.5.2 to 9.0.4PearPC can run various PowerPC OS's but in Mac terms it can run OS X and nothing earlierThere's also Executor which can some 68k software on an x86 computer.I guess Basilisk II and vMac would work, but keep on mind that those emulators will emulate Motorola Macs (no PowerPC, no Intel), so they will work up to MacOS 8.Pear PC emulated PowerPC Macs, but only worked with early MacOS X (and it's support is limited).They are all getting to be dirt cheap now but if you decide to go the G5 route, stay away from any model with liquid cooling. It is estimated that PearPC emulated Mac OS X at 1/10 of system speed (so a would run as fast as a but it doesn't take in account better CPU architectures (now a i7 core running at 2.8 Ghz has more power than a P4 at the same speed, and most CPUs are now multicore).I've installed Mac OS 7.5 in Basilisk II and it worked, but I hadn't applications, so I don't know how well it behaves.Also, I've installed Mac OS X in Pear PC, and it worked sluggish (with a 1 Ghz AMD CPU, it behaved as expected). Powerpc 9 Emulator Software On AnAlso, I made a disk image from a running iMac (266Mhz with Mac OS 9) and tried to load it in Pear PC but it didn't run. MacOS 9 was abandoned in favor of of the Unix-ish NextStep/Openstep based Mac OS X. Like previous version, it lacks true protected memory or pre-emptive multitasking.

Mac OS 9.x, based on Mac OS 8 was the final product based on the classic MacOS architecture.

How to emulate mac os 9 on windows 10