bridging with ad hoc wireless network

We are trying to bridge an Ethernet network (three computers on it) with an
ad hoc wireless network (two laptops). One of the two laptops is supposed to
be the bridge as it is connected to both networks. The single networks work
perfectly when separate. As soon as a bridge is made, no communication flows
in any direction.

The bridging computer is running on xp (service pack 2)
Is it perhaps not possible to bridge with an ad hoc network?

Thanks for any help