get a 6600gt with 128mb of RAM from eVGA.
DVI is digital video input. it is a way of connecting a monitor to a graphics card. SLI is scallable link interface it is a way of connecting 2 pci-express graphics card in one computer to make it faster. that means you have to buy 2 identical cards to use it. you NEED neither.
next time do a little research on these forums or at
www.tomshardware.com or
www.wikipedia.com before you post obnoxious threads