It is build right into the timeline now, no need for scripts.
Open Blender and select the default camera.
Duplicate the camera and move it to a new location.
Rewind to frame #1 and move the mouse into the timeline window.
Press the M-KEY to create a marker at the current frame #.
Move the timeline to a new frame # and press the M-KEY to create a second marker.
Right-Click on the first marker in the timeline.
Then right click on the camera you want to associate with that frame #.
Move your mouse into the timeline window and press CTRL-B. This binds the camera to that marker.
Select the second camera and second marker and do the same thing.
Now look through the active camera and press play on the timeline.
If you did everything correctly the first camera will switch to the second camera when it reaches the frame # the second marker resides at.
What is nice about this system is that you can re-time your camera changes by just moving the markers.