It is more than possible. OSx86 documents it pretty well, but then you need to dual boot to get into OSX and that is lees than ideal. I don't know what Goz means by flakey, OSX on a PC is identical to Mac, better sometimes (you have proper control of the underlying hardware, and are able to use BIOS to tailor it to your needs)
Natively? Like Wine? Unfortunately no, mainly because 99% of Mac apps aren't built againsy Mach-O only, they are built against Cocoa and all the other higher level code that Apple works very hard to protect. There are even device drivers built into every install of OSX that decrypt encrypted parts of Finder, iWork and various other 1st party Apps incase anyone was ever successful in natively emulating OSX and its frame works (see DontStealMacOSX.kext)
