1. probably a problem with java, do you get any error messages?
2. Advanced searching is not supported by the gnutella protocol.
3. With meta-data search you can try to specify more clearly what you are looking for, so you receive less 'bad' results.
4. Well, LimeWire tries to continue incomplete downloads but it doesn't always work because the remote host serving the file might not be available or LimeWire crashed and the downloads.dat file was corrupted.