|That's waaay too much video card for that old machine. You should be looking for a sub $100 card with low power requirements. 1 Gb memory is the most you will need for that machine. Your computer is probably worth about a hundred bucks or so and what you want to do is a complete waste of money.|
So, flying a little closer to earth...
1. Low power requirement card that does not require a power connection from the psu.
2. 512 Mb or 1 Gb video card memory. GDDR5 memory is preferred.
3. Less than $100 out of your wallet.
AMD HD6670 is a good choice. Imagine nvidia has a few decent choices too.