Unless you are a 64Bit operating system, which you do not mention, you will be wasting your money. 32 Bit will only see 4GB and use around 3 and a half GB.Ram limits
You mention your CPU as being AMD athlon ll 2x 2.9 Ghz Do you know what the three numbers are following the x 2? I think it might be 225 or 245
Another thing to think about is your PSU as a newer card will/might need its own power connection.
You do not mention budget either, which will obviously dictate where you can look for your upgrade.