Firstly you have to identify which type of card do you have? AGP (ACCELERATED GRAPHICS PORT) or PCI-EXPRESS? Seccondly I would recommend you to buy a single 512 mb DDR2 card of ATI (Radeon X1600 to be accurate) ( if having AGP) which is the cheapest product for what it offers. I bought it for 99 euros (150$) and I am very satisfied.
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Mike form Greece, 14