ppv

Hm.. i've been searching the threads about GTX280 vs 4870x2 which most of them i saw is 4870>280 but they were old posts.. can anyone show me a recently test? coz there's some drivers released recently..
I'm planning to buy/upgrade my pc, currently i'm using:
e8400
p5q
2gb ram
320gb hd
asus en9800gtx top (can anyone tell me wheter my card>9800gtx+?) ;o
psu crosair 750W
os : xp
What i have on my mind is to upgrade my OS to vista ultimate (best for gaming among the other vista right?), so i will have to upgrade my ram to 4gb (max on vista right?) and my display card dunno which should i get, the gtx280 or 4870x2, but as i know intel has corp with nvidia so probably nvidia?
last question does the MB affects the display card's performance?
thanks in advance
edit: why i want to upgrade is because when i play COD4 at 1600*1050 with everything set on max, i'll get some RED fps which i didn't expect for.. so i'll have to turn my settings to normal/low to have a good avg fps and play in a "smoother" way...