that you were/are logged on to an admin (rather than a limited user) account on that computer, then download and run the Norton Removal tool http://service1.symantec.com/Support/tsgeninfo.nsf/docid/2005033108162039 and reboot.
If that doesn't do the trick I'm not sure, but you could probably benefit from a manual search of everything Norton or Symantec on the computer and registry, making sure that hidden files are displayed. (folder options)
(Then, after you've tried AVG for a while, if it gives you any problems, try Avast, or Avira.Wink)