Onus :
What physical size is it? If standard ATX, you'll probably be limited by depth, but should be able to fit at least 550W-650W in there. If it's TFX, I think you can get up to around 400W.
spentshells :
what gpu and add on cards are you going to install?
Also as mentioned above what is the form factor of the case?
The case is an ATX. Height: 39.4 cm (15.55 inches)
Width: 17.5 cm (6.89 inches)
Depth: 40.9 cm (16.14 inches)
Also I am not sure which graphics card would be compatible im just running the onboard hd intel graphics, but if you could recomend a card also (preferable nvidia) I would appreciate it. I have 6GB of ddr3 ram, 1 terabyte hard drive, i3 2120 processor and am running windows 7