Function:   SetDisk()

               With SetDisk() you can change the current DOS
               drive to any other drive. this function uses 0 to
               indicate drive A:, and not 1 as many others do.

   Syntax:     SetDisk(<nDisk>)

   Arguments:  <nDisk> indicates which drive will be default. 0=A
               etc..

   Returns:    Nothing, check with GetDisk() if the desired is
               indeed the default drive.

   Usage:      SetDisk(2)          /* Make C: default drive */