For the record and after a long and dreadful search I want to add symptoms
and a solution:

Goal: have 2 LAN segments with different IP ranges on Alix.2C3 (3rd is
PPPoE/WAN)

Equipment: 	
- Alix2c3, BIOS version 0.99, running m0n0wall 1.3b14 (any 1.3b for that
matter)
- Dell Inspiron 8500 with Broadcom 440x 10/100 integrated ethernet
controller, Windows XP SP3
- Netgear 105 switch
- div. LAN patch cables cat 5e

Symptoms:
- connection on VR0 ('LAN') runs perfectly no matter how connected (direct,
with or without switch etc), so problem is not connecttion/cable related
- connection on VR2 ('OPT1') never worked, no matter how connected
- re-arranging the port assignement in m0n0 does not help ('OPT' never
works, no matter on which physical port), so it's not a hardware problem on
Alix
- 'never worked' means no full two way connection: pings from m0n0 to the
outside arrive correctly (verified with Wireshark), the reply doesn't
- any connection attempt from the outside is just ignored on 'OPT1'
(verified on all ports using nmap)
- I then installed plain vanilla nanoBSD (using GNERIC kernel, FreeBSD
7.1rc1 and no tweaks) - not a single connection on any physical port works!
- running tcpdump in nanoBSD I see that ping replies etc. from the outside
world make it into the kernel without errors - somewhere after reception the
packets get lost in the kernel (?)
- using a different Laptop (old IBM Thinkpad T21 with 3com NIC) - all of a
sudden everything seems ok
- fooling around with driver settings on the Dell: as long as 802.1p QoS is
enabled, it won't work with 'OPT1', but does work with QoS disabled

Solution/Conclusion:
- disable 802.1p QoS on the Broadcom 440x driver when using vr0 driver on
m0n0
- it is still a mistery to me why it works without this on m0n0 'LAN' port
though

Stefan