Generally with video editing the most important thing to look for in a card is the memory, something like the ATI 9800 256MB or NVIDIA FX 5900 256MB should do you proud, bit pricy, the NVIDIA FX 5600 is a cheaper option.
Keep in mind with tha above the rest of your systems got to be able to keep up with it!
TOny, I agreed on Techy. Get the 9800 ati Pro or XT and have it OC'd http://atitool.ocfaq.com/ . Make sure you have atleast 120GB 133HDD w/8mb cache, lots of MEM and fast CPU.