Easy
I'm assuming that you've already got the router/modem and the hardware fitted to the desktop and the lappys.
best to connect the desktop to the modem by a cat5e cable, as a wireless configuring can die halfway though and leave you unable to talk to the modem for ever......
set the DNS and Gateways on the modem, desktop and lappys as follows:
modem DNS 1.2.3.4
gateway 255.255.255.0 (same for all)
desktop DNS 1.2.3.5
lappy1 DNS 1.2.3.6
lappy2 DNS 1.2.3.7
lappy3 DNS 1.2.3.8 etc etc........