That's what it is supposed to do.  There is no way to maintain two separate connections at the same time.  The one with the lower metric rating (0), in this case the wired connection, will dominate.

There must be a way. It works on all other systems I have tried it on. I've even done it with two 10/100 NICs plus a wireless card. They were all desktop systems, but I do not believe they change the wiring on notebooks. I do not think it is an OS problem either since all our machines run Win XP Pro fully updated.

Of course you can. This has been the prefered and recommended way to achieve routing and bridging (ie internet sharing) since Win98 or earlier... One NIC to the DSL/internet/external network, and one to your home/office network. And, as I have stated before, I have it running on several machines already - both wired/wired, wired/wireless and wired/wired/wireless combos. The only problem is that these notebooks behave differently. I think it must be a driver or setting issue.

There is no way to pull in two IP addresses into the same machine at the same time.  One has to take precedent.

Now that you state the issue correctly, I see what you are trying to do, but with wireless?  Which connection is the wireless card handling, internal or external?  You'd be better off settings an access point off the first NIC.

Well, actually that was an oversimplification to visualize the type of problem...

Actually we have the following scenario:

We are putting together a measuring system which must be light weight (air transport as carry-on luggage, hence the notebooks), easy and quick to install at various factories (hence wireless between server and clients) and connect as securely as possible (timeouts/dropped communication unacceptable) to the ADAM measuring devices (hence wired from client to ADAM). We also do not know in advance the distances, so the kit will include one AP and one repeater per client. We should be able to drop the AP and run in ad-hoc, but keeping an AP makes it simpler to connect to our network back at the office.

I have a new lead which might actually solve the problem. Will test it and post my results here...

It seems like you need to force specific (unique) IP addresses on all network cards (wired and wireless) to make it work in the notebooks. After creating the network bridge you also need to force a unique IP address for the bridge (ie setting wired NIC to 192.168.123.2, wireless to 192.168.123.3, make the bridge, set bridge to 192.168.123.4). On all other systems I have installed this everyting worked using automatic settings...