If you haven't done so already, grab the latest version of the program from ZDNet Downloads.
After you've installed the Gnutella software you'll be greeted with the GnutellaNet screen. But you won't get very far without doing some configuration. So head over to the config section.
By default, the program will save files you download directly to your desktop, making them nice and easy to find. The "Path(s) to files" field lets you choose what, if anything, you want to share with the network. We've added our main MP3 directory - Gnutella automatically adds anything in any directories under the ones you specify, so make sure you know what you're sharing before you just start typing in random paths. For instance, you really wouldn't want to share any files that contain your passwords, or other sensitive material, since anyone using Gnutella could possibly get hold of it.
The only other item here that you may want to alter is the connection speed. This won't actually alter your line speed - it's just a friendly way to let other Gnutella users know how fast your connection is. So enter 56 if you're using a 56k modem - or, if you fancy yourself some sort of idiot, just enter some random numbers here, like 69, 666, or 420.