Diagram (also attached):

http://media.admirald.net/ofdiagram.png

I have both a nice internet connection and a corporate intranet
connection that also has access to the internet. I would like the LAN
to be able to access both but ONLY access the internet over the good
internet connection (on WAN), NOT the crappy-speed internet hooked
onto the intranet (OPT1).

The LAN uses 10.0.1.0/24 and the Intranet uses 10.9.0.0/16 and 172.30.0.0/16.

Can I do this with m0n0wall? If so, how exactly would I go about
setting it up correctly.