No point in adding more ram, with a 32bit windows install, as the 4gb limit is shared with the graphics memory. Get on 64 bit Windows first, then get the ram. Your power supply will dictate what GPU you can use. I would want at least a GT 730, with GDDR5, like this one.
something it's called money now please please answer to this question will this work on my mother board? yes or no?http://www.amazon.com/G-SKILL-PC3-8500-Channel-240-Pin-Desktop/dp/B000XXUUXG/ref=sr_1_13?
Check the ram configuration you have now. If it is 3x1gb, pull the stick that is by itself and get the numbers off of it, and try to find a matching stick. If it is 2gb and a 1gb stick, find the 2gb and buy a matching stick to that 2gb. Mixing ram brands can cause problems.
You should be able to find the same model number of ram, on ebay. I have done it for OEM rigs, such as yours before, hence my recommendation. It should come out a bit cheaper that way as well, since you would only be buying a single stick of ram