// in WinMain
dlg = CreateDialog(hInstance, MAKEINTRESOURCE(DLG_MAIN), NULL, dialogProc);

while ((result = GetMessage(&msg, NULL, 0, 0)) != FALSE)
{
    if (!IsDialogMessage(dlg, &msg))
    {
        TranslateMessage(&msg);
        DispatchMessage(&msg);
    }
}

// done



// in the dialog proc
	switch (msg)
	{
        case WM_INITDIALOG:
            // init stuff
            return TRUE;

        case WM_COMMAND:
            switch (LOWORD(wParam))
            {
            case CMD_BUTTON:
                // here's where I want to disable input to the main dlg window,
                // launch my new dialog box, have it complete, then return
                // control to the main dlg
                EnableWindow(dlg, FALSE);  // is this necessary?
                launchNewDialog();
                EnableWindow(dlg, TRUE);
                return TRUE;
            }
        }


// now for launchNewDialog

// parent hWnd is the dlg
newDlg = CreateDialog(GetModuleHandle(NULL), MAKEINTRESOURCE(DLG_CALCULATE), dlg, calculationProc);

while (!done)
{
    // check if there are messages to process
    if (PeekMessage(&msg, newDlg, 0, 0, PM_NOREMOVE) != 0)
    {
        while (PeekMessage(&msg, newDlg, 0, 0, PM_REMOVE) != 0)
        {
            if (msg.message == WM_QUIT)
                done = TRUE;
            else
            {
                if (!IsDialogMessage(newDlg, &msg))
                {
                    TranslateMessage(&msg);
                    DispatchMessage(&msg);
                }
            }
        }
    }

    // here's where I do my calculations
    calculationFunction();
}

//and finally, the newDlg's proc
switch (msg)
{
case WM_COMMAND:
    switch (LOWORD(wParam))
    {
    case CMD_CANCEL_CALCULATION:
        DestroyWindow(hDlg);
        return TRUE;
    }

    case WM_DESTROY:
        PostQuitMessage(0);
        return TRUE;
}