网络上有很多利用VB编程实现屏幕变暗的效果（像关闭Win95时的效果），我用VC改写了一下，权利属于原文作者！
正文
    HDC hdc;
         //屏幕的宽度个高度
    int SCRWidth,SCRHeight;

    if(m_Bool)
    {
    BYTE bybits = {0x55, 0x0, 0xAA, 0x0,
                     0x55, 0x0, 0xAA, 0x0,
                     0x55, 0x0, 0xAA, 0x0,
                     0x55, 0x0, 0xAA, 0x0};

    hBitmap = ::CreateBitmap(8, 8, 1, 1, bybits);
    hBrush = ::CreatePatternBrush(hBitmap);

    hdc = ::GetDC(NULL);
    SCRWidth = ::GetSystemMetrics(SM_CXSCREEN);
    SCRHeight = ::GetSystemMetrics(SM_CYSCREEN);

    ::SelectObject(hdc,hBrush);
    //0xA000C9
    ::PatBlt(hdc,0,0,SCRWidth,SCRHeight,0xA000C9);

    ::DeleteObject(hBrush);
    ::ReleaseDC(0, hdc);
    }
    else
             //重画整个屏幕
        ::InvalidateRect(NULL, 0, 1);


正文完，本文源代码：

  http://www.vchelp.net/ASP/ibr_upload/656.rar