How to setup 2nd NIC and route that traffic thru Virtualbox guest

[len mccoy]

I've setup Virtualbox and TOR using a how to article from this site and now route all Virtualbox traffic through TOR using middlebox.sh from the article. I use Ubuntu 10.04 as both guest and host.

Now I'd like to connect an additional physical machine with a second network card and route it's traffic through the guest OS so that it is anonymous as well.

I've done some searching and can't find anything (that I can understand as a novice) that would guide me through this. I've looked a many articles that talk about setting up Linux as a router, but none seem to fit my particular needs.