It's all up and working now. Rather than add the DNS entries in the resolv.conf, I'm sending it straight to the client using the dhcp-option:

--dhcp-option=6,8.8.8.8,8.8.4.4

Thanks again for all your help, 9k!

Have you looked into trying to put something together using dbus scripts rather than the widget? http://wiki.maemo.org/DbusScripts

It looks interesting. I tried running it in debug mode to take a look at events that the xoom might trigger when connecting to the n900, but I didn't see anything pop up in my initial testing.