i can take a guess thats its overheating when the CPU just drops to just above idle. and i run Norton Anti-Virus 2007 every weekend so i dont see how- Wes
i wouldn't assume that a cpu dropping to idle is due to overheating. you can pop the cover off, ground yourself out, and feel the cpu (actually the heatsink) with your fingers. if it is very hot to the touch, it is overheating.
but your cpu temps may be normal when this behavior occurs. if temps are normal, the wacky behavior you describe might be a trojan or virus not detected by Norton's, esp if you do not update your virus signatures often.
after years of using Nortons I switched to
Bit Defender due to very good reviews. I find it catches things missed by Norton. I highly recommend it, and it is less of a resource hog. I also recommend Spyware Doctor to go along with it, its a high quality application, updates almost daily. always use a good firewall too.