Virus Protection Change?

I am now using Norton Internet Security 2007 and my computer is not running as fast as I would like it to. I do download music which may be part of the problem, but the annoying thing is that when I run a full Norton system scan, no viruses or spyware are ever found. Then when I run a good free scanner like BitDefender or ewido, they find a bunch of malware. Why can a free scanner find these problems, yet an expensive software like Norton cannot? Should I delete Norton and go for a free software combo like AVG + SpyTerminator, or should I stick with Norton?

Virus Protection Change?virus protection

Avira Anti Vir

Spyware terminator

and Ad-Aware

plus a good fire wall

firefox with WOT and SiteAdvisor

is all you need.

Virus Protection Change?agv

I have two machines with Vista and two with XP and the latter are down for repairs and the Vista gets hit too. A registry cleaner can find stuff in there but they are not free. I am suspicious of the OS companies or company of raiding our sets. I ran one rebuilt PC from Goodwill and soon found the OS after me and they closed the Hard drive down to one action only... Get registered. I now see the modem and the hard drive have give away numbers on them and need to be matched etc. Keep disc clean and defragging after a total power down.
Since you've already payed for Norton,I'd first get in touch with their customer support and try to resolve your issues. Once your subscription runs out,I would switch to AVG. As far as anti spyware, I think using a combination of Ad-aware, and Window's Defender are probably your best bet. You can find these at www.cnet.com.
Spyware/Malware and viruses are different. Viruses can cause serious damage to your system whereas the former are usually more of an annoyance (and a privacy risk).