Also you will see less ram when running a 32 bit copy of any windows flavour as 3.25 gb is the max 32 bit can address. To increase performance and make full use of your ram at that capacity and above you will need 64 bit copy of windows. This in itself will increase capacity but you will need to ensure your graphics card etc is 64 bit driver compatable,which to be honest 99.99% of gear from 2002 onwards is.
Just by a fresh install alone you will notice a jump in performance and I advise windows 7 home 64bit as the way to go.
I run a similar spec pc that I built a long time ago with intel components and will play any game even crysis(however I run two monster graphics cards) but you will not need these if you run the games you stated.
The only downside to 64bit used to be the software from certain company's was never written in 64bit but nowadays that is a thing of the past and anyone who tells you not to go 64bit is scared of change and not likely to ever think of updating there os anyway. Trust me it's a good move.
Milky