What version of Limewire did you have? LimeWire Basic is free and can be downloaded from the official site:
http://www.limewire.com/english/content/download.shtml.
The pro version costs $18.88USD and can be purchased from the same site.
If you had pro and it's not past the 6 months, you can redownload it by putting in the e-mail you used to purchase it here:
http://sales.limewire.com/support/pro_lookup.php
If you got LW from any site other than the official one then you may have been scammed. See this thread for more info on scam sites:
Membership? - **WARNING ** BEWARE** - Download p2p Clients ONLY Thru Official Sites