It seems like the best thing to do is to at least wait until SP1 before taking the vista plunge. I am running a dual boot with XP and Vista, but still do all of my gaming on XP. This will probably change when I get hold of a DX10 card though..
If money is no object, I'd say spend a bit more and get a GTX from a brand with a large warranty, BFG and eVGA have 10 year warranties - you never know you might need it. Either way, 1 year from OcUK is a bit short.