yes the 20 steps are applicable on the three computers.
i suggest that when you go to http://www.j79zlr.com/cablenutXP2k.php to calculate your ccs, use the MTU value of 1500 for PC 1 (Server) and use MTU 1492 for both clients (PC 2&3).
note (i don't know if this is applicable to you): K9 web security slows down your internet connection but not noticeable. for security purposes, however, it is necessary to install it especially if you're operating a computer shop.