Update: Apple 'Boot Camp' Software Boots Windows On Macs: Dual-Boot Apple OS X, Windows XP, PC Magazine, 04.05.06, By Mark Hachman and Michael Miller.
Just in case anyone missed the news, it's available from Apple. Beta- and unsupported but will(?) be added to next Mac OS release. The above brief "news flash" tells a bit about what it takes to use it, and where you can get it.
A more complete description is at Booting Windows on Macs: Why It Matters by Micael Miller. (Linked in the first article above, but has a little more detail and some commentary – and "reader comments," so anyone really interested may prefer to start here.