Joe,
For about the same amount of money you can do one of the following:
Buy a second hard disk, replace your existing HD with the new one, do a clean install of the O/S (I assume you have access to installation CD), then progressively add back applications until the problem re-occurs. Of course, if the problem appears straight away then it probably IS your system. You can return your original disk to get back to your starting point.
The second approach is to buy RAM to replace what you have. If the system runs perfectly with the new (and you have changed nothing else), then it points to a RAM problem.
The point is to buy judiciously, so that you end up either with a RAM upgrade or a useful 2nd HD - or both!
My money is on a software issue. I find that webpages with Java scripts are a killer on my system, as the AV software goes into overdrive and everything stops for a couple of minutes, after which normal service is resumed.
Actually I just find that Java runs like a dog all the time!
SD