Turn wireless on, depending on what laptop it is there will be a switch on the outside somewhere that looks like a little aerial with lines coming off it.

Then right click on my network places on the desktop, go to properties, right click on wireless network connection, select "view available wireless networks"

youll then get a list of networks in range, select the right one, then (if youve set it up properly) you'll get asked for a network key/passkey...enter this in both boxes and away you go

Your wireless key you should have a note of somewhere, if you've got a bt voyager router it is on a sticky label underneath the voyager box itself