windows machines cannot see the Airport (or the attached USB drive)

I added an airport extreme (5th ed) to my ethernet network to extend the wireless reach. When I map the network, the Airport is not there and I cannot access it by going directly to the IP address. Everything else works fine through it and I can use the Airport utility to access it. I just want to get to the USB drive that the utility clearly sees is there...but I cannot, any ideas why it won't play nice?