AppleScript, Network preferences help

The easiest way to do this is to create a new Location in System Preferences -> Network.

Configure this location with your specific IP address requirements, then you can just switch locations to activate the appropriate settings, either via the Apple -> Location menu, or via a simple shell command that you can call via AppleScript, like:

do shell script "scselect Location_Name"

(where Location_Name is the name you gave to the Location in System Preferences.)

Clearly you could have another script revert to your original settings by just substituting the appropriate location name. If you're adventurous you could even have the script prompt the user to select which Location setting to use or, even more advanced, have the script check which config is in use and switch to the other automatically.