I have long since uninstalled my Limewire with all those junk I was getting. Recently, an urge to have new songs on my player rose. This got me researching on "safe, free music download" which got me reading loads of forum threads. Lots of websites came up.... but then I got to one post telling the asker that Limewire was OK as long as you know how to set its options to avoid getting searches that might contain viruses and other bad stuffs.
From here, I jumped from post to post getting great insights on the topic. Basically, MP3 is too small a file to get any virus to come with it. The worst thing you'd get is an unfinished song or those that got advertisements inserted.
What you have got to be wary about are zipped files, xls and xls files.
Then again, another problem... I was looking for OPM but could not find sources to the search results. Searched again and found http://www.oonly.com/
So far, I have downloaded about 10 OPM songs which are of great quality. So this comes highly recommended. Luv it!