I've downloaded limewire on my mac and it lets me search for songs and
download them but it won't let me launch them I've tried downloading limewire
5 times now and each time the same thing.

I could be way off but you might want to try playing the songs with another program.

Another thing to check is if you have limewire using its own player in your options. I can't be sure but it may well be that limewire won't play music if you have its mp3 player de-selected.