According to MSDN’s documentation for Sleep:
A value of zero causes the thread to
relinquish the remainder of its time
slice to any other thread that is
ready to run. If there are no other
threads ready to run, the function
returns immediately, and the thread
The important thing to realize is that yes, this gives other threads a chance to run, but if there are none ready to run, then your thread continues — leaving the CPU usage at 100% since something will always be running. If your while loop is just spinning while waiting for some condition, you might want to consider using a synchronization primitive like an event to sleep until the condition is satisfied or sleep for a small amount of time to prevent maxing out the CPU.