I have antivirus and antispyware in the background. Sometimes ill scan a file if i've downloaded it from a site that i'm not sure of -- just as added confirmation that there isn't anything in the file that shouldn't be.

The way a good antivirus is supposed to work, is to prevent infected files from getting to your computer in the first place, so the antivirus is supposed to hook the file before the operating system does, and deal with it then (copy new file/ access file/etc). Then it can clean/delete/quarantine it -- i used to know how some of the programs worked at a higher end technical level, but its been a while since i had to actually do any program work with Norton - i'm always surprised at the amount of things i forget

Even more important than manually scanning with an AV is making sure that the program is updated -- as with spyware programs as well. The program is only as good as its most current update, and since theres always new problems out there, keeping up to date is important