I use one PC and two laptops. The laptops are wireless capable, the PC not so. I use a wireless modem for internet service access and want to use a wireless router for file sharing purposes, but not internet sharing (move modem from machine to machine as neede). How do I need to configure?

First question WHY so convoluted ?
Simply attach all the devices to the wireless router and job done.
Or employ flash drives for smaller files..

If you use a broadband modem, there are routers you can plug the modem into. But I agree with CurlyBen. Just use a wireless router and simplify your life.