Need help sharing macbook wireless internet connection with pc notebook

I have a Macbook running OS x version 10.5.8 which is connected to the internet via Verizon usb760. I want to share that connection with my Sony pc notebook running Windows XP pro using the built in wireless card. I have setup the airport correctly and I have had success running an ethernet cable between the two computers and I can get the mac to show up in the available wireless connections and attempt to connect but no matter how I try to configure it I can't get the pc to connect to the mac wirelessly. I would be very grateful for some assistance. Thanks.