WinXP on intel Macs. Kind of.
While everyone's still unable to boot either Windows XP or Vista-betas on their intel Macs, there now is some success
doing it via linux. It's now possible to have an intel Mac boot into a Knoppix live system which runs WinXP via VMWARE.
The "real thing" is still missing, though. Because Mac users will either want to run VMWARE directly on Mac OS X (without having to leave OS X and boot into linux) or reboot into WinXP directly. But progress is progress nonetheless.