New Computer

512MB memory means nothing. Memory plays a part yes, but clock speed, bus width, and pixel pipeline count, are the major players. Look up some reviews too, just in case.

Looked up Crossfire on SLI boards, it seems that ASUS made a BIOS update to make the drivers not block crossfire if it is attempted on an nforce4 chipset...

I did do some research on the card, here are the specs.

SAPPHIRE Radeon X1600PRO
Core clock-500MHz
PixelPipelines-12
Memory Clock-780MHz
Memory Size-512Mb
Memory Type-GDDR2

More infomation here
http://www.sapphiretech.com/en/products/graphics_landing.php?gpid=133