>what about the right edge and the bottom edge of the screen ?
Something like

IF Thisform.Top + Thisform.Height > _screen.Height
	Thisform.Top = _screen.Height - Thisform.Height - ;
					SYSMETRIC(9) - 2*SYSMETRIC(4)
ENDIF	

IF Thisform.Left + Thisform.Width > _screen.Width
	Thisform.Left = _screen.Width - Thisform.Width - ;
					2 * SYSMETRIC(3)

ENDIF