WM_ENTERIDLE fuSource:MSGF_DIALOGBOX  hwnd:001b11dc
WN_SETTEXT lpsz:000BEF18("SHELLY TO DO.txt - Notepad")

[Open dialog sends the following things]
WM_COMMAND wNotifyCode:BN_CLICKED wID:IDOK hwndCtrl:004F092E
WM_NOTIFY idCtrl:1148 pnmh:000BEB30
WM_NOTIFY idCtrl:1148 pnmh:000BEB6C

[Tada!]
Use ::GetOpenFileName or ::GetSaveFileName passing pointer to a OPENFILENAME structure.