it should be printed on the side of the PS. you'll have to pull the side off the case and look at the sticker..... however, if you're only using a 17 monitor the PS will probably already be big enough because the graphics card won't need tons of power.
try a Radeon 6770 or 7750 or something in that performance area. neither card needs an external plug for power.
edit. you should run 4gigs of ram. it will help your system out. try and squeeze more of what you already have ( exactly ) or buy 2 - 2gig sticks that are compatible with your system and discard the old stuff.
Hey Swifty Morgan,
Thanks for your response. I had tried to use 2X 2gig cards but for some reason unknown to me the memory reads only 2 gigs. May be it is incompatible. So I had removed one card and left alone the new 2 gig card.
Also I have a spare 1 gig card can i use this along with the other 2 gig card.