It kinda just worked for me, I didn't need to inf mod or anything. I'll do more proper testing soon. I did notice a weird issue running Java, but I'm not sure if that was from transferring the SSD with XP between like 4 different machines before ending up in the laptop.
I have a M4800 upgraded with the M2200, it appeared to work under XP but I didn't get around to testing any 3D applications. I would suggest getting something Ivy Bridge, 8570W/8770W or M4700/M6700 for better XP/Vista compatibility
Depends on your laptop, if you have the option, go for it. But if it's a Dell it should've automatically disabled it when in XP, because that's what my M4800 did.