LimeWire multicasts queries to the local network but it's neither quick, nor easy nor fool-proof to configure it to run without any connections at all.

If you have an almost static local host to connect to, you could use LimeWire with some modifications to the default configuration. The default configuration - if your users should be able to use LimeWire out-of-the-box - can be found in the source code and requires compiling & packaging the modified LimeWire version yourself.