Actually, have a look at http://www.gnutelladev.com. There's a section of published Gnutella code, and you can find some VB versions around there. Could either continue building on top of it, or use it as an example.

I'm not a VB programmer though, but I know that VB is quite well capable for writing a Gnutella client. The now defunct GnOtella client was written in VB.