Got it to work at last…
Reasons for the trouble were two things.
1. The documentation says theres no filtering between bridged interfaces. But I have to set a rule on the OPT1 interface to allow all traffic to all nets like this to make it work (especially for DHCP request).
Proto Source Port Destination Port Gateway Description
* * * * * * OPT1 -> Any
So there IS filtering between bridged interfaces.
2. Flaky Wlan driver on the client side. Nasty Netgear WG511 PCMCIA Card. Forced it to eat a newer driver for an 3Com Office Connect Card and works now without problems and even has AES support now.
So for all people with the same problem:
If you want to create the following setup:
WAN -> Internet
LAN -> Local wired network
OPT1 -> AP Wireless LAN bridged to Local wired Network
just do the following
-Get your WAN and LAN running. Then go to the OPT1 settings page and set it to be bridged with LAN. Leave the IP configuration for the OPT1 interface to static.
-Setup the remaining wifi stuff (WPA,WEP,Keys etc) and save the settings.
-Next go to the Firewall Rules settings page and click on OPT1 interface. Add a new rule to allow traffic from any to any.
This did the trick for me.