A 32-bit operating system will only see 4gb of ram in total.
That includes ram on things like a soundcard (some Soundblaster cards have ram) and your video card(s).

Looking at your system, video is not an issue for 5-boxing.
The processor will work fine, although a Q6600 can easily be overclocked to 3.0 ghz and are a lot cheaper then going to an i7.
I'd really look at more ram, 6gb as a minimum and 8gb is more preferable.
For more ram to work, you'd need a 64-bit operating system.
Windows 7 seems to be far superior to Vista or XP.