I use wifi to access the internet through my ap, which is directly connected to my cable modem. This means Ican browse the internet etc, without having to turn my pc on.
If you want to access the net through a pc, your have to set it up as a NAT (network address translation) router. I think this can be done through the ics(internet conection sharing) wizard. Basically you have to bridge your network connection.
I used to use this to connect my linux box to the net, but got really p***d off as the windows box kept dropping the link, needing a reboot to fix it. I also had to turn on two machines to access the net.
If you have a wifi ap, then do yourself a favor and buy a wifi cf card. Then you can lose the usb cradle and surf without having to boot your laptop.