quickly enable/ disable web access

HI, I am very much of a novice user. I have a quad 2.5 PPC tower( 150 gb raptor boot, Quadro FX4500, 4.5 gb non ecc ram, Highpoint Rocketraid 2320) It is running Mac OS X server unlimited client 10.4.10. This machine will be providing the IP addresses for 25 client imacs running Mac OS X Tiger 10.4.10 I The internet feed will be coming through one of the gigabit ethernet ports and the other will be providing services to the clients. I would like to be able to cut off web access simultaneously for all clients(middle school students) and yet retain access to the web for myself all the time. I also need them to retain access to the shares on my array all the time though. Is there a script or a command to perhaps disable port 80 simultaneously on all clients. Or is there a better way to accomplish my intent.