go with the x800, i have a 6600gt and i have a friend that has a x800 and it beats mine. not by much but it still beats mine.
CPU-Intel Pentium 4 630 3.0Ghz / 2MB Cache ~~OS Windows XP SP2
MOBO-Gigabyte 8I915P Duo Pro Intel Socket 775 (PCI-E)~~HDD-Western Digital 160GB(SATA)
PSU-Aspire 500W ATX~~RAM-1GB PC3200 DDR SDRAM (512x2 Dual Channel)
GPU-MSI GeForce 6600 GT(PCI Express)~~Monitor Viewsonic VA902B 19" 8ms~~ ATI TV Wonder Pro (TV Tuner)
~~Still to come~~: eVGA e-GeForce 7800 GT