Sounds like your audio files have QuickTime player as their default program. You need to change it to iTunes. See How to change default program in OSX & use iTunes as the program to select for both mp3 & m4a files.

As for your firewall issue, we need more information; System details - help us to help you (click on blue link)

Make sure your OSX firewall is configured or turned off; OSX Firewall settings for Tiger. However your firewall problem might be your modem/router.

Thanks for your help, Lotr. I did as you suggested: both reconfigured my firewall to permit Gnutella/Limewire access and changed the default program for opening sound files. Now, when I select a downloaded file in Limewire and click "Launch," iTunes opens but nothing happens. The track in question doesn't show up, and the silence is deafening.

Any further ideas?

Thanks again for taking all the time and trouble you take to help technological idiots like myself.