If i was too choose between thosem i would have chosen the 9800 one since it have a better clock speed. Although the 9600 one have more memory i still think that the 9800 would be superior.
I think there is a 9800 1gb on the market if you would like it. But also "AND PLEASE DO NOT MAKE SUGGESTIONS ABOUT ATI RADEON,as i said i only have these two choices! " Hmm i guess you hate ATI.
Why? Guess it is a "if you got Nvidia and is happy with it, you can never go ATI" problem... wich just is dumb! I dont take either Nvidias or ATI's side, although i would recommend you to check up some ATI cards since they are on the same level of graphics for around the same buck.
Take whatever card you like the most, but if these two are your only choice i would say the 9800 card.