public enum KeyStates
{
    None,
    Down,
    Toggled
}

public bool IsKeyDown(Keys key)
{
    return KeyStates.Down == (this.GetKeyState(key) & KeyStates.Down);
}

private KeyStates GetKeyState(Keys key)
{
    KeyStates state = KeyStates.None;
    short k = GetKeyState((int)key);
    if (((int)k & 32768) == 32768)
    {
        state |= KeyStates.Down;
    }
    if ((k & 1) == 1)
    {
        state |= KeyStates.Toggled;
    }
    return state;
}