As long as the antivirus program scans things before read/write/execute then you dont need a special POP3 scanner.
The new version of AntiVir sucks because you can't easily dissable the memory-resident scanner. Plus I liked the old Windows 95 look compared to the 'lets look like bullshit' look.
Also, memory resident scanners make your computer SLOW. As long as you keep Windows up to date, you shouldnt need antivirus, unless your a moron and click everything you ever see.