Make a cmd file called sleep.cmd:
REM Usage: SLEEP Time_in_MiliSECONDS
@ECHO off
ping 1.0.0.0 -n 1 -w %1 > nul
Copy sleep.cmd to c:\windows\system32
Usage:
sleep 500
Sleeps for 0.5 seconds. Arguments in ms. Once copied to System32, can be used everywhere.
EDIT: You should also be away that if the machine isn't connected to a network (say a portable that your using in the subway), the ping trick doesn't really work anymore.