I prefer to "not" install the norton AV... viruses can only enter by using flaw (in OS, browsers, softwares) or if the person who use the PC allow it to (clicking OK blindly, opening bad mail attachment, etc)... installing AV is bad for my small CPU resource =þ
while spybot/ad-aware is useful to clean up "bad" cookies, because we have to allow cookies if we want to browse the internet normally...
last time I install a `running on background AV` on this PC was 3 years ago and I never have a single virus since then... I do online virus check in trendmicro or panda ocassionally, also never find one...
what I do is just keep my OS, browsers and softwares updated... and of course being wise while browsing the internet...
so I really don't understand why the specialist don't like spybot & ad-aware :D
* there is a possibility that spybot/ad-aware will ruin some programs including the norton AV (cmiiw) but having a spyware by installing it is just not true, unless maybe you're getting the software which has been modified by someone...