1. Buy the laptop and but a wireless PCI card for the desktop PC.
Install the wireless PCI card in the desktop PC and run the network setup wizard on it to enable file, printer and internet sharing.
Run the same network wizard on the laptop.
You can then connect to the internet via the desktop machine as long as the desktop machine is switched on.
2. Buy the laptop and buy a wireless ADSL router.
The router will replace your current ADSL modem. Plug the router into the desktop computer with cable supplied and run the setup (you will need your ADSL account details handy).
Now, run the wireless utility on the laptop and it will pick up your wireless router. You can then add encryption to it if necessary once everything is working.
This option means you can use the internet on the laptop at any time without the desktop being switched on.
With both options, you can share the printer and install it on the laptop meaning you can print using the printer connected to the desktop as long as the desktop is switched on. It also means you can share files.