简单的抓取屏幕生成位图文件（不用内存图象拷贝API函数）

Private Declare Function BitBlt Lib "gdi32" _

  (ByVal hDCDest As Long, ByVal XDest As Long, _

   ByVal YDest As Long, ByVal nWidth As Long, _

   ByVal nHeight As Long, ByVal hDCSrc As Long, _

   ByVal XSrc As Long, ByVal YSrc As Long, _

   ByVal dwRop As Long) As Long

Private Declare Function GetDC Lib "USER32" (ByVal hWnd As Long) As Long

Private Declare Function GetWindowRect Lib "USER32" (ByVal hWnd As Long, lpRect As RECT) As Long