Read about one MacWorld staffer's experience installing XP on an Intel-based Mac Mini in this article. Conclusions: it took way longer than he thought it would to get it running, now that it's running it works, it's missing a few things but is fine for most apps, a couple of the glitches can require a clean reinstall with loss of all data on the disk, he wouldn't bet the farm on it yet.

If you plan to try it, this article is a must. Lots of practical warnings about the gotchas, as well as things that one might think are going wrong but are just how the process works.