Based on the motherboard having an integrated Geforce 6150, it's safe to assume that your CPU is a socket 939. Finding socket 939 AMD Athlon X2's are quite difficult nowadays and even if you do, they are usually pretty expensive for an "upgrade".
I think a video card would be your best bet for improving performance for your current system, mainly for freeing up resources (CPU cycles and RAM). Doesn't have to be anything fancy either.
I think a video card would be your best bet for improving performance for your current system, mainly for freeing up resources (CPU cycles and RAM). Doesn't have to be anything fancy either.