Video card question

Hello, I need to ask a question:
I want to change my video card because my current card is not wery good for games like Half-Life 2, Doom 3 F.E.A.R......
I have two options:
1. A 6600GT or TD with 128MB 128 bits DDR II (GPU 4XX MHz and the memory 900MHz.
2.A 7600XT 256MB DDR II but the frequencies are litle bit lower than the 6600.
Now the question:
Witch one should I chose?

Here are my specs:

MB:Mercury KOB KT266a FDSX
CPU: AMD Athlon XP 2200+ @ 2000MHz 256MB cache 266FSB
RAM: 1GB DDR PC 3200
Video card: nVidia GeForce 6200A 256Mb DDRII (375MHz GPU/535MHz RAM)

THANKS

CRISTI