In the webadmin panel, go to "Advanced" -> "Configuration" -> "Network" -> "Firewall" and check mark the box that says "Disable Firewall"...
After that, i'm not sure how to enable the automatic detection. I just had one network card so, the virtual NICc it creates is your internal .1 address and the actual interface gets served an ip adress from the DHCP server running on the virtual NIC, the end result is both NICs being in the "internal" subnet of the whole setup, and detection worked fine after disabling the firewall. If you have a different setup, i'm not sure.
Once you disable the firewall, you can manually add your network shares, i've done it this way also and it worked ok. There is a wiki article on manually creating network shares I believe...