You'll need a wireless access point or router, and a wireless card for both PCs.
You do not need to have an Apple base station to make this work. ANY router or access point that conforms to the 802.11 standards (it should mention WiFi certification too) will work fine. I'm partial to Linksys products, but Netgear, D-Link and others are just fine.
The PCs can use a PCI wireless card and connect wirelessly quite well. Or you could get USB wireless devices for them-there's a lot more USB wireless support for PCs than for Macs. The PCI cards require you to open the case of the computer, whereas the USB devices don't.
I would go with one of the "known brands" for your third party choice. Linksys, Netgear, D-Link, and Belkin are pretty much safe alternatives, but "Joe's Storm Door and Wireless Company" should be avoided. Going with name brands is a Good Thing for support and reliability.