The price is paid once and it will include the right for 6 months update of the program as well as tech. support. After that you can update for a smaller fee (something around $ 14 - $ 15 for another 6 month); but you don't have to.
Just make sure that you save the installer.exe of LW at a save place in case something happens to your installation.
And please download and purchase from the official site, so you'll get the real LW Pro.
http://www.limewire.com/ 