I've always had good luck with Norton knocks on wood desk. The only thing I don't like about the new version is the God awful Norton Protection Center :Z . Thankfully, the service can be easily disabled.
I admit that on older, slower PC's, trying to run Norton is typically a fool's errand. On my kids PC (a PIII-550 box, with 384MB RAM) Avast is the way to go. I'd hate to even think of what NAV 2006 would do to it after how painful NAV 2003 was on it.