Gnutella is pretty easy to block. Simply drop all packets to destination port 6346 & 6347 and no connection to gnutella will be possible anymore. As an alternative you could scan outgoing packets for the line
"GNUTELLA/0.6 CONNECT" and drop them. The effect will be that you will never make a successful connection and there is nothing you can do if your admin has the slightest clue of what he's doing.