Using Script To Randomize Sites?

Here is what I want to do. Create four or five different versions of my site and when someone goes to it a randomly chosen version is displayed. The way I was thinking of doing this is to have the index page of each version in a frame, the containing would run a javascript that choose one of the versions of the site. I figure the container would not display anything and just be a tiny portion of the screen with no visible frame.

That said, I don't know anything about javascript. I just assume this is what I would use to do something like this. Does anyone have a better ideas as to what I would use for this or ideas on how I would go about doing it?