hmm - Let me think.
What about those who have 3 cameras or 5?
Each cam can have a different frame rate - what frame rate would you use for the split screen stream, the lowest or the highest of all cameras involved?

With a bit of html you can easily place the four cameras on one page.
If you want the images to update you can use the java applet - that is probably easier than to modify the JavaScript page.
If you're using Firefox you can use the mjpeg streams without java applet also (sometimes a reload is required to get them going), IE cannot display them.