I've been using XP 64 for about a year with an Nvidea Quadro 3450 which is Open GL.  Works good.  Already running the 64 bit version of Vue on it, although Vue 6 is still only pre-release.  Also using the 64 bit version of Cinema 4D R10, but sadly that product has an export problem for now so I have to use the 32 bit version for exports.  Poser 6 is also running ok under it.  

Vista is definitely something to wait a while for, just do a google search on it and problems on the screen fill up fast.  There are several versions of Vista, each with their own price.  Go to www.windowsvista.com and you will find a lot of information from Microsoft about its features, editions, etc.  But don't go for the hype yet, Microsoft always makes things look better than they really are, espeically on new things.  Waiting for SP 1 or 2 sounds like a prudent move.