upgrading acer power supply

I am normally fearless with building and upgrading my own personally built rigs. But I bought an Acer Aspire M5100 w/AMD Athlon 64 X2 4400 with the stock PSU, and am toying with the notion of upgrading the video card, but with the stock power supply, I cannot even power up the current crop of cards.

I am looking for guidance in this area, from anyone who may have upgraded their wimpy PSU's and what are my limits with the Mobo I have here, and I realize that I could build my own rig for almost the same amount of money, but I am trying to, in this current economy to keep my costs down as best as I can.

Any advise or information would be greatly welcomed. Thanks.