which operating system(s) the machines are running, and this can make a difference. Ideally at least one of them will be running Windows XP, which will make things easier.
What you'll need are two wireless network adapters. The Laptop can have a PCMCIA card type - Linksys make an excellent one - and the PC can either have an external USB wireless adapter, or an internal PCI wireless card adapter.
Install the adapters and run the software that comes with them. Then run the networking wizard in Windows on both machines. If one machine has Windows XP it will offer to make a floppy disk which you can use to set up the network on the other machine.
Make sure both machines have the same workgroup name - by default Windows will offer MSHOME as the name - and that both machines have unique names on the network, any name will do, as long as they're different.