Engadget is pointing to a compelling video [video link] of Windows XP booting on an Intel-based iMac.
You may be familiar with the contest offering a bounty for
this feat. If narf2006 (the author of this video) has in fact
gotten the job done, he's about 12 grand richer. We'll see what happens.
AppleiMac 27-inch with Retina 5K display (late 2014)