If the whole code uses 100% CPU power then why do you assume it is from the Sleep() function? Or you actually mean you tested the Sleep() function and it uses 100% CPU?
If you haven't tested it you can put like a big value to Sleep() and make a program executing only Sleep() and see what happens. How to you see how much CPU the program uses?
I don't know any other function btw. I would say that Sleep() shouldn't use much CPU. Judging only by the name and its description http://msdn.microsoft.com/en-us/libr...98(VS.85).aspx
But it might not be sophisticated at all...