Read about the XP DMA issue at http://forums.cnet.com/5208-6122_102-0.html?messageID=3234381&tag=mncol;lst;2#3234381
Be sure to toggle that.
Now about your post. This might not apply but I am not finding any words about this machine. It could need its yearly dust bunny patrol. Watch the video at http://reviews.cnet.com/4520-11319_7-6240575-1.html
My computer last night started loading slowly. For example I have New STALKER game it usually takes 1 min to load a level now takes 8 minutes, it still does this after i did disk cleanup and defraged drive. I was going to do disc check tonight as it took over an hour just to complete 5% of phase 4(again runnng slow). I don't even know if that will help. I tried loading TF2 to see if it was just STALKER and it loaded unusually slowly too. I have no viruses as I've scanned my computer and it was clean. Boot up seems to take much longer as well between 4-5 minutes. I don't have programs to load on start up so that isn't the problem. It didn't gradually get worse it went from loading fast to 8x slower immediately.