X2 runs like a dream here on XP 32. I would have to say more stable than X1 was. I'm planning a duel boot xp/7 soon with a SSD but mostly for EWQL samples and DX 11 gaming support. I briefly tried 7 and X2 with the a patch on a standard HD here, it ran well, perhaps loaded more quickly but the only other thing I noticed differently was my DX plugs were not there to use and some of my vst plugs were not loading.
I'm sure I'll warm up to 7 since DX11 is so wonderful for stereoscopic 3D gaming.
I guess it boils down with how you use it. If your projects are like mine, mostly live recorded tracks with a few VSTi's for drums and bass. I think you will be OK with XP for now.
If you're planning on large projects consisting mostly of high end synths such as EWQL and some IK patches. XP will quickly run out of resources on you.