well, for the legal opinion, that's for the lawyers.
LimeWire is a site that offers software that allows individuals to find and share each other's files. This is known as "p2p" software, for Peer to Peer file sharing.
LW doesn't decide what files people share, so as you can imagine or see for yourself quite quickly, some people share files that are illegal--the kinds eagerly discussed in Gr 4 playgrounds. Many share legitimate files, but legitimate uses of p2p software don't get much press or attention.
Click on the LimeWire icon at the top of the page to read more and evaluate the software.
As far as I'm concerned (like you I started learning about the p2p a few months ago), the LimeWire project that is developing the way for people to share the files they choose is fascinating and very worthwhile.
So there's a very rough answer for what it's worth.
Cheers