I think you would be better off uninstalling the whole thing and starting again. Norton can be notoriously fickle when uninstalling part components. Use the Add / Remove Programs facility in Control Panel to uninstall System Works, which may or may not also uninstall the Anti Virus and Firewall components. If not, you will have to uninstall those separately. When you reinstall AV and Firewall, you should install AV first, and your subscription status should remain, or you may even get a new subscription for another year, if you're lucky.
I note that you are intending to do an upgrade to XP, rather than a clean installation, and I have to say that this is not as reliable as a clean XP installation, as it may carry forward any problems you have had with ME. Have you considered doing a format and a new XP installation? You may find, in the long run, that this is the easier option.