I think maybe this was discussed before, but its certainly worth mentioning again. PearPC, a PowerPC emulator has been recently updated and now that it has been out for a while there are some handy guides around on how to get OS X up and running on your Windows box. You can check it out here:
Its not going to break and speed records, but it is certainly a neat platform to tinker on. I think it would probably benefit from systems with a bunch of RAM. My machine only has 512, so I can only dedicate 256 to it. In contrast, my 12'' PB has 768megs of RAM. Worth a go if you're interested, took about an hour and a half to get everything jiving, including networking support.
Yes Merlin, but provided it runs on the i386 architecture. OSX can't run on i386 platforms.
I've always been quite intrigued by these emulators... PlayStation emulators with hardware graphic acceleration through Direct3D, PearPC and of course VMWare.
The problem with these things is not to emulate, but to emulate and be still fast. Some pretty crazy coding at the core, I reckon.