How do I know which type of ram I need?

Here you go man, this is some good ram to get, I know it's 2 gigs but it's at a nice price and It's good quality ram.

http://www.newegg.com/Product/Product.aspx?Item=N82E16820231114

I went from 2x512 to 2x 512 x1 1024 so 2048 ram now but my computer doesnt feel any faster but I did install it correctly since dxdiag says i have 2048 ramshonosuke08

Probably won't notice much unless you run some games that take advantage of it.

I did that same upgrade with 2x512 to 2x512 + 1x1024 to 2gb, but one game wouldn't load. I looked at my mobo manual and it said not to use all 3 dimms at once or the computer might not start. And then if the RAM's different in size, brand, etc. use dimms 1/3. Not saying you'll have problems, but might wanna check the manual if you haven't. I ended up getting another 1gb of same, put the 2x512's aside, so have 2gbs 1x1024 + 1x1024 and runs fine and dual channel again.