Hmmm sounds like you have been scammed if you paid for the basic version. LimeWire Basic is free. Check out this sticky in another forum here.
http://www.gnutellaforums.com/showth...threadid=28751
Where did you get your LimeWire basic version from?
The Official LimeWire Website can be found here.
http://www.limewire.com/english/content/download.shtml
The "nag" as you call it is part of the basic version, and as far as I know cannot be disabled.