Well I use Norton Internet Security 2004 and I can honestly say that it is totally hopeless. Autoprotect is meant to automatically scan files that you open/use on your computer right? Bah, I think its just a waste of RAM.
Another thing thats annoying is the Proxy program that it runs. If ever at all it fails, your internet will not function without it no matter if you shut down Norton. You have to reset your computer (which for me running 256SD) is quite some time.
The worst thing is when Norton actually manages to find viruses, it then 90% of the time proceeds to tell me that it cannot delete the file/s. What a load! I can go through and delete them with ease, yet Norton has all these *problems*.
Asides from Norton and its hopelessness, I use Spybot Tea Timer which is a great program for blocking unwanted registry keys. It picks absolubtly everything up and nothing goes un-noticed
I also use Microsoft Antispyware beta 1 and its also pretty good. It weeds out a few malware/spyware files that Spybot doesnt run and has a good range of advanced settings.