The programs themselves aren't illegal but how you use them may be a different story.

Depending on your country's laws, downloading/sharing of copyrighted material might be illegal.
For example, here's LW's copyright information: Copyright Information - Lime Wire
Use Google to search for your country's copyright laws, or use the forum search to look for legal, legality or something similar - chances are you'll find threads with more info.

Files shared on the Gnutella network can't be controlled by the client that you're using - anyone is free to share anything, so infected files can be shared.
I don't know about 'Limewire Turbo'. But LW (official version) gives you the option to check files with Bitzi before download: http://www.gnutellaforums.com/open-d...owse-chat.html

The latest versions of LW have measures in place to delete files that are known nasties, before they're saved to your HDD.
But it's still ultimately up to the user to scan downloaded files with their AV app/s before opening