Vista is a no brainer if you have a c2d, 2 gigs RAM, and a nvidia 7 or 8 series GPU. Anything lesser then please back away slowly lol.
I can also vouch for crappy marketing, take this official MS comparison of DX9 vs DX10. The shot on the left can easily be done on DX9, and since it is such an old shot, it was probably done in DX9 in the first place. They compare it next to 7 year old Halo to make DX9 look bad or something. Very deceiving and childish.
http://www.gamesforwindows.com/en-US/About...irectX10-a.aspx