You will need some wireless networking kit. You will need some form of wireless router. You might find its worth investing a all-in-one solution which includes router, wireless router, modem and firewall makes life a lot easier when setting it up. Currently some deals around at the moment that would allow you to connect your desktop wirelessly as well.
For the kit
click here with free laptop or desktop wireless adapter.
Remember if you mix a wireless G and B network it will only run at the range of the slowest components.
A quick search for wireless should reveal more.