Just butting in here.
Trender, you can drop to a 600Watt powersupply, make sure it has at least 1x6 pin and 1x8 pin (or 1x6 and 1x6+2 pin) PCI-E connectors, quality makers are: Antec, Corsair, XFX, OCZ, Silverstone and Seasonic.
One point, you might want to look into getting a better CPU cooler and overclocking your processor, even a modest overclock like mine (3.4GHz) makes quite a difference in CPU heavy games.