|"No prob in psu as I have a 600W one!"|
Wattage isn't as important as amperage. Plus the power supply needs to be made from quality components. There's a huge difference between a $20 generic 600W PSU & one from a reliable manufacturer such as Antec, Corsair, Thermaltake, etc.
As for the memory used on the graphics card, it has nothing to do with system memory. Decent gaming cards will have DDR3/GDDR3 or DDR5/GDDR5. Cards with DDR2 are generally lower end. And the memory buswidth is very important. Gaming cards will use 128-bit or better. Cards with 64-bit memory are not good for gaming.
Also, the memory limitation for 32-bit operating systems is not a rumor, it's fact. Here's an old explanation:
This article should help you choose a video card:
Best Graphics Cards For the Money: March 2011