spmcbride1201 :
I believe that gaming performance would be most economically improved by upgrading the RAM and the GPU. However, my impression is that AutoCAD is much more CPU intensive. You could possibly look at upgrading just the CPU and using it with your current motherboard, as I believe that AM3 and AM3+ CPUs with work on an AM2+ board. That could give you a performance boost and allow you to keep the CPU when you get around to upgrading the motherboard as well.
agree!!... upgrading DDR2 RAM for a 4GB 1600 RAM DDR3 could increase the performance
but if you are able to buy mobo and CPU could be a great improvement, but you could save some bucks if you buy 1866 or 1600 RAM...
also i have used autocad 2D mostly, and you dont need nothing special, even with your actual rig you most have a good performance (except for the RAM)
if you want to use your system for rendering and design programs, nvidia ussually gives a better performance with game hardware