Want to upgrade my pc but I forget everything about computers lol

I built my pc a couple years back and only put in 2gb of ddr2 ram at the time. Now with the release of starcraft i notice that my load times are super slow and it was suggested that more ram would help. Also during play i run at 95-98% usage.

anyways current specs (from cpuz and gpu-z)

windows xp 32 bit. I suppose i could get windows 7 64bit but i like that utorrent runs without problems for me currently. I heard that my friend who has windows 7 has numerous problems with it working. along with other programs
2x 500gb wd hard drives
q6600 @3.0ghz
asus maximus formula x38 mobo
nvidia 9800 gx2

** 2048mb ddr ram

frequency- 400mhz
fsb dram 5:6 (fml i just remembered these were supposed to be even.. i dont even know how to do that)
4
4
4
12

2T



Anyways with my current motherboard and setup what is the best ram i could get? and if i were to get 4gb how much would my pc use? (due to xp 32bit)


thank a bunch and any additional advice would be greatly appreciated.