There is a way to have XP on a Sandy Bridge machine. Get a copy of VMWare's Fusion 4 and install it. Fusion can do a clean install of XP or work from your Bootcamp partition. I used the Bootcamp option which took about 10 minutes to set up. XP boots and runs flawlessly. There are no missing drivers in device manager. Windows boots faster in Fusion than it did from the Bootcamp partition, probably because it's not searching for drivers.
I know, I know, XP is ancient and over a decade old, but some of us need it to run old software. If you have a new Mac and need XP this is the way to go.
[crarko adds: I presume you could do the same with Parallels. I admit to never being a huge fan of Bootcamp, with good VM options available. Now Apple, please let us install Snow Leopard legally in a VM on Lion (or Mountain Lion).]

