Advice on Graphic card for Minor HD editing Cant Decide

Hello,

My pc is a Gateway LX6200-1 AMD Phenon 9500 quad 2.2 w/ 8G ram, Vista 64bit and a 400/500 PSU, the built in GPU is a shared Radeon HD3200 w/ 512 mem. I do a little bit of HD recording from console gameplay (Avermedia HD DVR HDMI PCIe crad) as well as video camera and such. I need to upgrade my graphics card to something dedicated but do not need to go over board on power and price. The HD3200 works fine but I am having issues with a stutter, freezing video and laggy playback on preview... rendered videos come out fine. I just know the 3200 is tapping all my RAM as I need to reboot every 30 minutes if I am working on a large project with many vids opened in the workspace.
OK now to the question..

Would I benefit from a 1G Ram card or would a dedicated 512 be enough?
I have been looking at the Radeon 4670 1g DDR3, which honestly is in my current budget but people I have talked to say I need something more powerfull and modern and they recommend the GTX 460.. My issue isnt so much the money $50 diffrence between cards) but the draw on my PSU... the 4670 draws 59W as opposed to the GTX at 120ish as well as all the bells and whistles.. mind you.. I do not play PC games at all and I am talking about maybe editing birthday parties... recorded games, personal videos... stuff like that

If maybe someone can give me some advice on a acard or the memory issue... any maybe recommend some cards in the $75-$150 range, that would be sweet..

Thanks in advance...

~ John