BCGControlBar Pro for MFC
void CBCGPDialog::EnableExpand ( UINT  nExpandCheckBoxCtrlID,
LPCTSTR  lpszExpandLabel = NULL,
LPCTSTR  lszCollapseLabel = NULL 

Enables expanding and collapsing of the dialog's part.

nExpandCheckBoxCtrlIDIdentifier for the expand check box control. This check box control will have a special "Expand/Collapse" look.
lpszExpandLabelThe expand label.
lszCollapseLabelThe collapse label.

The expandable area contains some additional controls that initially hidden and appear only when user clicks "Expand" button located in the dialog bottom. The framework resizes dialog window according to the expandable area height.

To add this feature, simply create a new check box specifying start of the expandable area (this check box will be automatically converted to "Expand/Collapse" button) and call EnableExpand method.

Important: you cannot use this feature along with resizable dialogs or property sheets.