How much of the RAM does the System page show as being usable?
There's a very good chance that you simply are looking at the amount actually in use - my system rarely gets above 2.5GB in use, unless I'm running VM's, even though I can have 20 IE windows, and anything up to 20 other (minor) apps in use.
There's a good chance that all you need to do is install a decent set of drivers for your sound card, or remove an interfering program.