Desktops do not usually have a wireless adapter, but check in device manager (Right click My Computer, Properties, Hardware tab, Device manager) under network adapters. These are pretty cheap and go in any available PCI slot.

Thanks. I checked and I dont have one, ill buy one as thier cheap like you said.

One thing you should keep in mind is that not all computers have to connect to a wireless router by wireless.  If the computer is located within easy reach of the broadband modem and router, it would be preferrable to connect that computer to the router by ethernet.  Nearly all wireless routers have 4 ethernet ports.  Only computers that will roam about or are located in areas where it is inconvenient to run ethernet cable would need to be connected by wireless.   I just thought I would mention this in case you were unaware of it.

Steve