really shouldn't be complicated at all. Wireless ethernet bridges tend to be absolutely trivial to setup.
I wish I knew why it wasn't working then. I set it up, each side says it connected to the other. But packets don't seem to get through =/
What's on the other end? Have you SSH'd into Tomato and looked at the logs yet? Its biggest failing at the moment is adequate error reporting. You may want to take a peak for yourself to see what it's doing wrong.
By the way, the way these things SHOULD work is that you end up with a true Ethernet bridge, just like a rather low-level VPN. Should be seamless and work just fine, given a connection to the WAP. That said, if you can't get anything figured out there are dedicated wireless ethernet bridges out there for a pretty minimal cost.
-Sean