This feature is already in most of today's Gnutella clients. It's called an 'Ultrapeer'. You set one computer as the Ultrapeer and set the other clients as leaves and you connect the leaves to the Ultrapeer. The Ultrapeer is connected to the Gnutella network and processes all of the search results, etc. The Leaves send the searches and stuff to the Ultrapeer and the Ultrapeer directs the searches to the rest of the network. Then the search results come back, through the Ultrapeer, and then to the Leaves. Some clients that support Ultrapeers:

BearShare
LimeWire
Shareaza
Gnucleus