For what it's worth, I also use Avast home, and it's very good. Other worthy freebies include Avira, and AVG. (see the sticky on free programs)
There is an uninstall tool for Norton, available from the Symantec website.
I remember getting similar error messages on the new PC when Norton was on it. It never ran right, and I removed the program long before the subscription was due.
XP has a built in firewall, which is adequate for most safe surfers. For added protection (ie: including outbound) a different firewall is wise. I use Comodo.