The answer in PHP is the usleep function. The format is usleep(*); where * is microseconds, not milliseconds as in flash actionscript 2, etc. Sometimes windows folder renaming works without this, unless you are flipping folders a-b and then you need to name a to a_temp and b to a, then a_temp to b. Inbetween you should give the computer a moment to do the mechanical task presently in rotating hard drive 5400-7200 rpm systems running multiple core motherboards with windows xp-vista-7. Sometimes when you're on a shared server, the lag is even worse in this process, even in linux, unix, etc, those shared servers are still susceptible to this problem. Use usleep(*);, you're not in that much of a rush, are you?
