Wireless networking will work fine on a mixed platform network.
You can get Airport cards for your portables, or all of your Macs, or you can also use many other brands of wireless cards.
I believe that the Airport base station can bridge an Ethernet and wireless network together to make it seem like one network. That way wireless and wired computers can share files, etc.
The base station should use the PC as it's gateway(router) and the wireless computers should use the base station as their gateway(router).