Are you using windows xp by chance?
if you are, please realize your computer is actually only accessing like 3.2 GB of ram. it cant access the full 4GB. So if you have shared ram on top of that you have a lot less. I know Skype takes up 1GB, Haven takes up another 1GB. before my other computer fried itself I couldn't take a Skype call and be on haven at the same time, I would run out of ram. and that's using a dedicated video card, not shared like it sounds you are.