Control Panel sends the CPL_SELECT and CPL_DBLCLK messages when the user selects (single-clicks) or double-clicks an application icon. For each message, Control Panel passes the application number in lParam1 and the lData value in lParam2.
Typically, an application DLL responds to the CPL_SELECT message by doing nothing. When it receives the CPL_DBLCLK message, it transfers control to the appropriate dialog box.