Need a PHP script

I want a small PHP script that redirects every X visitor to a different URL.
I need to be able to modify the X variable.

Example:
Four different visitors arrive at site.
All four click on the same link.
3 of the four go to url A
the fourth goes to url B

... ongoing (not as in a traffic cut-off limit)


Thanks

my bid:-$50 (50% upfront rest after you see a working demo on my server)
Turn around 24 hours
Thanks

If you search around you can actually find some for free, g00gl3 is your friend.