Further to this...when you do a full system scan, Norton suggests you first disable the "system restore" feature in Windows XP.
Windows may have made a backup copy of the virus and stored it in the "restore" file...this file is inaccessible to antivirus software.
Once you have done the scan....make sure you enable "system restore" once again.

Doing any of the above is at your own risk......

In youth, we learn....with age, we understand.