Becca: Having Pro does not make downloading copyright material any more legal.
Many people however are feeling that a pro purchase is a good way to show support for Limewire. Some, including me, say it works better than basic, and some don't, but if you buy Pro now, you will be able to keep it, provided you save a copy safely, for as long as you like.
(computer crashes have a way of wiping out your precious files and programmes, and you should always back your valuable data up regularly.)
Just to emphasise what 6pac said, Napsters problem was that it worked from a central server. Gnutella/Limewire do not, so will not go quite the same way as Napster what ever happens.
The latest Limewire information available about the case can be found at
http://www.limewire.org/blog/