It would take a AM3/AM2+/AM2 board to reuse the DDR2 with an AMD quad. I used two of these with my wife's and her mom's computers.
The board and cpu I proposed were AM2 and used DDR2. I do this for a living I would not offer a solution that would not work with his ram. You can buy an AM2 quad core cpu and matx AM2 motherboard from tiger direct for $99