dx10 is not backword compatable with ANY older version, vista runs dx9L(longhorn) and dx10, dx9 dosnt run better on vista, do a clean 2k/xp/2k3 install and a clean vista install then test dx9 games on each, under a current system my exp is that at best it runs the same, at worst it runs a bit slower, but drivers are a problem with vista, since nobodys got RTM drivers ready yet
funny how nvidiots alwase say they didnt/dont care about aa+hdr till they get an 8800, not trying to be insulting but its a fact, seen people who spent the whole time since the x1k cards came out saying hdr+aa is useless and pointless, who now have 8800 cards and are all stoked about hdr+aa and how its the best thing in the world.......
i love my x1900xtx(about to flash toxic bios to it!!! i have tested both sides cards.
my video card histtory.
s3 virge3d(icky card) and a voodoo1 and pvr pcx2(matrox m3d powervr card)
voodoo rush card(2d card and voodoo card in one)
rendition verite 8mb+m3d+v1(great cards)
riva128+2xm3d+v1
tnt1
rage128 (horrid 2k drivers, its why i learned to HATE ati)
tnt2 ultra
geforce1
gf2gts
kyro2(great card)
gf4
fx5800ultra, wost card i ever owned, good/decent dx8 perf, HORRID dx9 perf, slower then a card 1/4 its price)
radeon 9600 256mb non-pro, replaced the fx5800ultra(aka dustbuster from hell) and out performed it in every way at 1/4 the price)
9800se 256bit(hard moded to pro)
6800gt, sold this card within about a month of buying it, nvidia couldnt seem to fix the driver problems with quility and perf, aa/af falloff neer center of the screen really bothered me so did the 5sec studder.
x800pro vivo>xt pe(flashed to true xt pe) still have this card, its faster then the 6800gt was overclocked to ultra, no driver buggs to speek of, just a great allaround card, still got it in my backup box.
x1900xt/xtx 512mb, got this after trying a buddys 7800gtx,7900gtx, and 7950gx2 cards at his house against his x1900 card and finding that i felt the quility was better on the 1900, also the aa+af issue was important to me, since nvidia couldnt do it.
i have also owned other 6 and 7 seirse cards but they came to me via trades and the like(got some at work from systems we replaced for people after they died also) they are "ok" but i would take my x800xt pe over a 7800gt anyday
also the fact is that ati's x1900 based cards(x1950/x1650xt) are more powerfull then their nvidia equivlants in newer games, and can also be used for folding and boost decoding(and can be used to boost encoding as well) of video data, again to me this is important, it shows the cards got a future, and when its not good enought to use for video anymore it can be moved to use as a PPU!!!!!