Hi Soapy there is a few ways that this can be done.
1) Buy a hub (bout £50 or summit) what this would enable u to do is, to plug ur laptop into the hub using a CAT 5 ethernet cable and plug ur pc into the hub, again using CAT 5 ethernet cable, therefore allowing both to 'talk' to each other.
2) Buy a Cross-Over ethernet cable (no more than £10) what this would enable you to do is to connect the laptop and the PC together using the same cable...!
3) if you already have a Cat 5 Ethernet cable, buy an adapter to convert the existing cable to a cross-over (see above...!)
4) Buy a router with a built in switch, what this will enable you do is connect the laptop and the pc to your router, thus enabling the two to 'talk' to each other and if you have broadband connect to the internet!
I will post some links to give you an idea on prices...!
Hope this helps...!