will require a wireless network adapter - either an internal PCI type (PCMCIA card type for the laptop) or external USB models by Belkin or A.N. Other.
I suggest that you buy a Linksys wireless access point, and use it to distribute the wireless network.
Start the Internet sharing wizard on the machine with WinXP, and when it offers to make a floppy for use on the other machines do that. Then use the floppy to configure the other two machines.
It's actually easier to do than to describe, and if you follow the WinXp prompts it's difficult to go wrong.