I ordered an XP "downgrade" box from Dell just yesterday. It was just a tick box on the OS list, and didn't add any cost or force me to jump through hoops.
Speccing the same machine through Lenovo's website was a little more painful, but still doable. Looks like XP will stay around for a while.
That's weird, as I just purchased a simple Dell machine for our office today and I had an additional cost of around $100 to downgrade to XP. It wasn't a special XP box, just the Vostro so perhaps that is why.