Have you tried System Restore? Did this download start on its own or did you have your preferences set for automatic downloads? Both McAfee and Norton have a bad habit of believing they know what's best and they will often download without warning. In fact, it was a simultaneous, unrequested download from Norton and Microsoft's SP 2  at the same time that blew my XP system so bad I had to dump it. I have tried both applications and both are very intrusive and extremely overbearing if you dare question their superiority. AVG Freeware, which you can get for free from the net is a pretty good ststem that you seldom notice is running.

Good Luck.

Powell