Network Bridge Setup Problem

I have a small LAN with a windows domain. Very vanilla setup with a
Router, switch, 802.11G AP, a server/DC and some workstations &
wireless laptop. Now I want to add a workstation using a wireless
bridge instead of either wired Ethernet or WiFi card.

The workstation works perfectly when connected via Ethernet wire. When
I replace the wire with the wireless bridge I can use the Internet
connection and can ping the server and all other machines, but I can't
see the other machines or shares in windows. (Windows Explorer hangs
for a long time then times out). Laptops using WiFi cards & even a
squeezebox work perfectly. Any ideas where I should be looking to
troubleshoot this?

It almost smells like a windows or compatibility or WiFi security
issue, but right now even those make little sense to me. Same
behavior with 2 different bridges.

TIA