MainDlgProc
BOOL CALLBACK MainDlgProc(HWND, UINT, WPARAM, LPARAM);
hDlgMain = CreateDialog(hInstance,MAKEINTRESOURCE(IDD_MAIN_320X240),hBack,MainDlgProc);
hDlgMain = CreateDialog(hInstance,MAKEINTRESOURCE(IDD_MAIN_240X320),hBack,MainDlgProc);