My sister wanted a new graphics card for Christmas. Her computer settled it by having the current video card die. She chose the Nvidia GeForce 9600 GSO with 1 G memory, based on reviews of people playing World of Warcraft (her favorite game.)
She has a Dell Dimension E520 which meets basic requirements for the card -- at least I thought until I opened the computer up and didn't see a 6 pin Supplementary Power Connector. On the box they list that it comes with a "1 x DVI-VGA adapter 1 x S-Video cable." Not knowing what that was I didn't open the box, but went in search of more information.
http://support.dell.com/support/edocs/systems/dime520/e... Based on this you would have to use an adapter from the P10 connector (4 pin molex) most cards come with an adapter that requires 2 x molex so you might be in a hard spot. If you go for a replacement card the HD4670 performs the same and does not need external power.