Samba Team member Tim Potter has written an article on using Samba with multiple network interfaces. The piece is a nice write up on how to set smb.conf parameters for multi-interface servers. From the introduction:

Let's assume that we have a server with two network interfaces. Say that one interface, eth0 connects to the company network 10.0.0.0/8, and eth1 connects to 192.168.1.0/24, a small private network within the company. For one reason or another, we want shares exported by Samba to be available on the private network eth1, but not visible to the rest of the organisation via eth0. The machine in question may be a firewall, gateway or plays some other sensitive role. In other configurations, you might want to avoid SMB connections over your PPP or wireless connection, for performance reasons.

For the rest of the article, see Multiple Network Interfaces with Samba.