On Mac OSX, is it possible to let the computer obtain a specific IP address (192.168.1.123) on wireless network #1, and let DHCP assign it a dynamic IP address on all other wireless entworks?
1) On-board-solution here:
Use System/Network/Location/Edit Location and configure two different Networks (i.e. Home & Elswhere). There you can configure different settings.
2) To automate switching between Locations you could try this solution:
Use a tool like Locomatic to automate the process of switching Location settings by network.