The makes your looking are great I use Belkin but there all as good as each other.
For a wireless Network 15m is ok so long as there aren't to many obstructions in the way.
What you need: 4 time wireless cards for the computers and one Gateway Access point. There very simple to set up just make sure that you set each PC/Laptop with the IP Address 192.168.0.2 for PC 1 then PC 2 192.168.0.3 then PC 3 and 4 increasing by one digit. Connect the ADSL/Broadband cable direct to the router switch on and enjoy.
On the Belkin 54g router which is 802.11g it is also backward compatible with 802,11b.