Downloading a file from the Gnutella network can't install a virus, worm, trojan horse, etc. on your machine. Only running an executable file can do that.

Always run a virus scanner on executable files before running them on your machine. Files that contain only data and no executable code (e.g. MP3, ZIP, MPG, JPG, AVI, MOV, GIF, WAV, etc.) are always free of virii.

An added point: just because an executable file tests free of known virus programs doesn't mean that the program is not dangerous. Any file--including HTML files containing JavaScript or VBScript--can potentially contain code that will damage your machine's file system.

Downloader beware!