Are you trying to hook a PC with no internet connection up through your laptop with the bridging built into Windows? I've done itin XP, but not needed to in Win 7 yet. It should still work though.
Many laptops have settings to automatically disable the WiFi chipset when a connection is made on the Ethernet port. It's done as a power optimization because normally you don't want to use WiFi if an Ethernet connection is available. You'll have to disable that before this works. Different vendors put settings in different places. Check the BIOS, Device Manager (properties of WiFi), or any vendor supplied power managers or optimizers.