You should let the MacSense router assign all of the network addresses and just run the airport base station as a bridge. You would do this in the Airport Admin Utility by going to the Network tab and making sure "Distribute Network Addresses" is NOT checked. Once you do that, the MacSense router should assign all of the IP addresses and each of your machines will exist in harmony on a single network.

As for the sharing part, I would recommend you just turn File Sharing on in your system preferences. It will work over TCP/IP without AppleTalk being enabled.

Chris