I looked up the specifications on the motherboard, and it said it does support dual core AMD processors.
For a new graphic's card what is your price range? The card that currently has the best price/performance ratio is the ATI 4850 for around $200 http://www.newegg.com/Product/ProductList....=Radeon+HD+4850
If you want something cheaper, the Nvidia 8800GT 512mb is still a nice card, especially since the price has been dropping quite a bit because of all the newer cards. I was looking through the 8800GT's and found this gigabyte one for only 100$. It also has a $30 mail-in rebate. That is a good deal, even though it's only a 256mb version. http://www.newegg.com/Product/Product.aspx...N82E16814125089
. If you want something higher in performance, get a 512mb version.
As you stated, you will need a new power supply. I would say don't go less than 400 watts. It might be safer to go a bit higher and get at least a 450 Watt though.
"I think there is a world market for maybe five computers." - Thomas Watson, Chairman of IBM, 1943