There isn't a way to scan a file before you download it, as far as I know.
You can do a bitzi lookup on the file, and see what other have said about it if there is any information available. check this link out.
http://forums.gnutelliums.com/showth...ighlight=bitzi
Also I have NIS 2004 and I have my anti-virus auto protect enable at all times. This is no guarantee that you won't get a virus, but it should catch most of them should you d/l one by mistake. Make sure your virus definitions are up to date, and check for updates frequently
search the forums on this subject and you will find even more information.