Shows[Hides] a step in the control
int ShowStep( int nIndex, BOOL bShow = FALSE )
returns the previous state of this step (0 = hidden, 1= show) or < 0 for error.
-1 if nIndex = 0, which is the Start step. You cannot control show/hide of this step
-2 if nIndex is the Finish step, again, cannot control show/hide of Finish step