The program itself, to my knowledge, shouldn't be illegal; however, downloading anything that's copyrighted technically is, and with the RIAA breathing down everyone's necks, I think your parents are probably right there...
I know that Kazaa will give you spyware, and I assume that it would be the same with Limewire...so no, I don't think it will give you viruses, but it will give you spyware, which slows down your computer and is just an annoying little b10tch. :razz: