You'll need a wireless router that either connects to the Internet directly via your telephone line or through your current DSL modem if it is a cable modem system. The wireless router will typically come with a built-in firewall to protect you from Internet nasties such as hackers.
Your wireless-enabled laptop should be able to detect the router once it is configured and then use the router for its Internet connection.
To hook up the desktop PC into the network, you'll need a wireless network card for it. This can be a PCI card, which you'll need to fit into a spare PCI slot inside the PC or, alternatively, a USB wireless network adaptor, which is more convenient and certainly easier if you don't want to open up the PC (assuming that you have a spare USB port of course). Once configured, you'll be able to scan for available networks within range of the desktop PC and then you can connect to the router to get onto the network in your home and then out onto the Internet.
I would recommend buying the same brand of network card as the router.
Once the network is configured, you can right-click on the printer and go to the 'Sharing' option to allow access to the laptop.
Hope that helps
You might also find parts of the following D-A-L article that I wrote about wireless networking useful:
http://www.d-a-l.com/articles/library/13.html
wireless network
