I have 2 desktop PCs and a laptop with Intel Centrino technology. I would like to setup a network for the 3 computers (with the 2 desktops in different rooms) where the laptop can be used wirelessly.

I'm not very clued up on networking and would appreciate some help from anyone who can tell me how to do this.

Cheers

There are many ways to do what you want. I assume that all computers should have internet access.
Here is what you need:
1. modem
2. Wireless router (you mentioned wireless for the laptop)
3. wireless network card for the laptop
4. network cards for the desk tops
5. network cbles for the desktops
First hook up the modem to the wall outlet or rather a splitter if you need one. Then connect the router to the modem. Connect the two desktops to the router and configure the laptop wireless network card.
There are many different routers out there, some with built in modems print servers firewalls etc etc.... choose well.
Hope this helps.