I'm taking this with quite a few grains of salt. Some guy has just posted pictures on Flickr showing an iMac (Intel) sporting some Windows XP installation screenshots. There's nothing there that shows XP has successfully installed, but if you pay him/her the $1,000 they're asking for a video of it all and they may provide it.
Technical detail on what EFI is can be found on the Intel site.
The title of this post is unashamedly borrowed from Adam Curry's Transmitters? We don't need not stinking transmitters line from his Daily Source Code podcast.