Limewire has no control over the content of the network. People are free to share whatever, so there is illegal/immoral content out there. You could try reporting it to such organizations as the FBI:
http://www.ifccfbi.gov or the Child Pornography hotline:
http://www.cphotline.org/. It's sick and disturbing but really all you can do is filter it from your results.
You can
search the forums on this topic. It has been discussed many times. Here's a good place to start:
http://www.gnutellaforums.com/showth...98&#post196798