If it weren't 5am and I hadn't just spent the past 20 hours rebuilding my computer I'd post the actual PHP code to accomplish exactly what s/he wants.
It's going to use the mt_srand, mt_rand and a couple other functions but is pretty simple to implement.
Lemme get a few hours of sleep and I'll post the full code up for yas.
My Kingdom for a pillow and a fully functional computer...