So you want to use Grisoft's AVG Free as your antivirus, but had Norton antivirus installed before, which is now proving more persistent than a flatulent release in a bath, with Symantec's whole convoluted shebang only compounding your woes? Well below is a simple sureshot way to get rid of Norton for good.

1. First, from Start –> Cpanel –> Add/Remove programs, remove every trace of Norton and its associated programs, which means scan through the list of installed programs for any item that says "Norton" or "Symantec" or "LiveUpdate" — for example "Symantec LiveUpdate" or "Norton AntiVirus 2003".
2. When you are absolutely sure that these vermins are gone, it is VITAL that you reboot the computer. When you are back into XP, delete the following folders manually — if they don't exist that's fine:

   	c:\Program Files\Symantec AntiVirus
   	c:\Program Files\Norton
   	c:\Program Files\Symantec
   	c:\Program Files\Common Files\Symantec Shared
   	

   Do a SHIFT DELETE if possible, the folders don't go into your Recycle Bin in that case, so they are gone from your computer for sure.

3. After the above, I usually clean the Windows Registry for any entries that are lying around stray. Get a Registry Cleaner like HoverDesk's RegSeeker (zipped download) and use the "Clean the Registry" option.
4. Once that is done and you have SELECTED ALL and deleted the stray items, reboot again. To be sure.
5. Norton should be gone when your machine is back up. If not, Symantec has a brute force utility called RNAV2003 — get it here, which ought to do the rest of the scavenging, but it shouldn't come to that.