Ah yes...XP is a big ram hog indeed.  That's the problem.  There's no hidden problem really.  You just simply do not have enough ram to run smoothly.  Buy some ram.  

  I like 
www.pcinfinity.net for my parts.  No shipping at all.  You pay a small insurance fee (like a dollar something) when you order, but that's it.  Getting a whole pc shipped for a dollar or two is a nice deal.