Sorry, I haven't ordered a X200 but have purchased a lot of T61s with the XP downgrade.
1. Of course the hardware will support Vista but I don't know if you can get the install from Lenovo. I dislike Vista so much I've never researched it.
2. The laptop should arrive configured with XP with all the drivers loaded. Make sure to run XP update & Lenovo update to automatically make sure that you have the latest revs.
3. There is a tool on the laptop to burn a set of Reinstall disks which will bring your hard disk back to factory settings in case of a nasty crash. Make sure to run this as the first thing you do, it can be a lifesaver.
3. (again) Lenovo makes great quality laptops, the IBM attention to detail lives on after the sale & I'm sure you'll be very happy with the new toy.