Well, I just got finished setting up m0n0wall in a virtual machine using VMWare on my Home Server. The motherboard has a network card used by the system to access the network, and I have two additional network cards dedicated to m0n0wall.
So m0n0wall runs as its own separate machine with its own network hardware on top of WHS. I'm also using Hamachi as a service, to do remote backups of my Mom's machine (I did the inital backup locally first.)
So far its working like a dream!