You have to use the array $CmdLine.
Explanation:
$CmdLine[0] = Number of elements
$CmdLine[1] = first parameter
$CmdLine[2] = second parameter
etc.
Your Script would look like this:
PROGRESS($CmdLine[1])
Func PROGRESS($sleepME)
ProgressOn("Progress Meter", "Mapping Drives...", "0 percent")
sleep($sleepME)
ProgressSet( 10, 10 & " percent")
sleep($sleepME)
ProgressSet( 20, 20 & " percent")
sleep($sleepME)
ProgressSet( 40, 40 & " percent")
sleep($sleepME)
ProgressSet( 60, 60 & " percent")
sleep($sleepME)
ProgressSet( 80, 80 & " percent")
ProgressSet(100 , "Done", "Complete")
sleep(500)
ProgressOff()
EndFunc