Follow the instructions contained in the readme.txt file. Gnutella allows you connect to certain networks and certain computers without limiting you to one central server like some products available for download. It isn't centralized. You only need to know of one working servant IP to connect to the network. Gnutella isn't MP3-only.
Any file type is supported.
N-Tella gives you all you need to get on the network and track down those files you've been looking for. These guys are really cool. They are tracking the latest news and happenings with the underground file sharing scene. Join their list of lost Metallica fans. ZeroPaid has their list of former fans.