he was right about the Mobo, but the Core 2 Duo e7400 could run more powerful cards without issues.
the issue is, if you want to keep the CPU, you'll have to get a LGA775 socket Mobo with PCI-e X16 slot (for the VGA), there are some of these still available (http://www.newegg.com/Product/Product.aspx?Item=N82E16813157337)
buying such Mobo, which is almost dead, will not allow you to upgrade to a better CPU in the future. so it is up to you.
regarding the RAMs, how much do you have? you will need 4GB RAM to play games.