If i purchased another pcie card say, 6800gt, or w/e with a svideo tvout will i be able to use it to capture? or is my x800xt a special case?
Probably the best consumer capture card is the ATI Theatre 550 Pro (and its Sapphire and Tul etc. rebadges.) It has an excellent comb filter and near-perfect levels at default. There's also the newer Theatre 650 but there seem to be some issues with that chipset. You never get the best capture facilities in a video (out) card, though the high-end Nvidias are not bad, they don't have that great comb filter though.