An ICS box acts as a router to provide protection from the multitude of vulnerabilities in windows. This is of course frequently kept up to date with windows update.
As to protection from viruses - nothing beats common sense. As a general rule I don't open attachments ending with ".jpg.vbs"
which makes 99% of email viruses useless. If I have any slightest hesitation about an executable I receive from someone, I use the windows "run as" feature to run it under a guest account. That way it cant edit anything on the disk, or any registry entries, making any malicious code ineffective. Call it insane, but I dont use an antivirus scanner - simply packing an exe with a compression program like UPX often defeats virus scanners, using common sense when opening files makes them redundant. I find running NAV in the background makes my computer more sluggish as it needs to analyse all executed code, and all data written/read from disk.