Calling NT function on pre-NT system

typedef BOOL (WINAPI* UpdateLayeredWinFunc) (HWND, HDC, POINT*, SIZE*, HDC, POINT*, COLORREF, BLENDFUNCTION*, DWORD);

UpdateLayeredWinFunc updateLayeredWindow = 0;
HMODULE user32Mod = GetModuleHandle (_T("user32.dll"));
updateLayeredWindow = (UpdateLayeredWinFunc) GetProcAddress (user32Mod, "UpdateLayeredWindow");