My friend has a Alienware x51 with a i7 3770 and a Gtx 555, he was wondering if he could put a Gtx 760 in his PC. He has the 330w PSU.
Not without a PSU upgrade...
Without a PSU upgrade, he wouldn't be able to. Tell him to grab himself a Corsair HX series PSU or something similar.. He'll be able to run one in his system then.
The cheapest and best PSU that could probably be had, is the XFX 550W bronze. It'll cover you for any single higher-end card, with room for overclocking.
There are other options, but they are usually more expensive, without being "on sale".
Good luck finding a psu that fit's in that junk its about the same size as a old xbox 360.
Tell him to sell it and build his own desktop
Should tell him to sell it as suggested above. He could sell it for about 600-800 to someone that dosen't know any different.