When I was trying to get rid of Norton my son (who does computer repair stuff for work) googled some program that he ran that identified all the Norton traces where he was then able to get rid of them. It was quite an ordeal. He spent probably 24 hours over 3 days trying to clean the system up.
The problem I had was Norton was almost too good. I was having all kinds of trouble with the Norton firewall (even messed up my access to the Disboards for a while). I've since been using EZ armour (from CA) for both anti-virus and firewall with good results. I've also installed Webroot Spysweeper which takes care of a lot of spyware type intrusions. I also run Ad-Aware and Spybot S+D every couple days.
But if you want to know what has made the biggest difference in all the virus/spyware battles is I now use Mozilla Firefox for my internet browser. It's free to download, uses a fraction of the memory and is not on the virus writers hitlist as it's not terribly widespread. Give it a try, I think you'll be plesently surprized.