well, Norton is a known resource hog, and this could be an issue of it. Youi could also have a bad install of norton. I'd contact the good people at Symantec, or, depending on how much time you have left on your Norton purchase, begin looking at other alternatives.
But I'd probably start with Symantec tech support. They actually have wonderful tech support, but I guess there's a reason for that.
thanks,
v