You need an ADSL Wireless Router/Modem and then wireless enable each PC. click here The main tower can use either an internal card or a Wireless USB adapter. Similarly the laptops will need either a PCMCIA wireless card or USB adapters. I notice that the laptops only have one USB slot so the cards would be better leaving the USB port free for a printer perhaps.
click here= for a router with one bundled USB adapter. click here= for additional USB adapters. Or cheaper one`s click here (I`ve used these and they`re OK - just not as robust as the D-Link but half the price roughly.)
PCMCIA Cards click here
The above are only examples but it gives you somewhere to start.