I'm looking for very rare files. If I delete my connections to get other "new" connections, am I "manually" searching more users this way? If I repeat this process, let's say 10 times, do I have more chances to find the files?

Changing the ultrapeers that you're connected to can make a difference to the search results that you see - different hosts conect to other different hosts & on it goes

Keep in mind that you can't search the whole network - it's just too big.

Try varying your search terms... look for artist or album rather than song title, director or actors' names rather than movie title etc. Also try the 'All Types' search.
Search at different times of day, as people in other time zones log on & off then files being shared will change.

You might find a few more tips here: How to find music

Uploading similar material also helps. Also browse anybody (if possible) who might have something similar but exactly what you're after. They themselves may be connected to more people with similar files, then your searches may find more of the files you are after. Don't forget to use the 'Get More Results' function, as this helps to extend the horizon of the search a little.

Maximum Horizon of LW or a Gnutella client program, & perhaps http://www.gnutellaforums.com/new-ph...tml#post321136 (particularly GregorK's post #4) give a brief description of the limitations of searches for Gnutella programs.