必须是在Windows2000以下的系统才支持SetLayeredWindowAttributes这个API,原理就是先找到窗口句柄,然后设置窗口属性

program opacity;

{$A TYPE CO OLE}

uses
  SysUtils,
  Window 

var
handle,AStyle:integer;

begin
  try
  if ParamCount<2 then
  begin
  Writeln('parameter must');
  exit;
  end;
  handle:=findwindow(nil,pchar(ParamStr(1)));//目前是找窗口的Text,也可以是找Cla ame
  AStyle := GetWindowLong(Handle, GWL_EXSTYLE);
  SetWindowLong(Handle, GWL_EXSTYLE, AStyle or WS_EX_LAYERED);
  if SetLayeredWindowAttributes(Handle, 0, strtoint(ParamStr(2)),LWA_ALPHA) then
  Writeln(ParamStr(1)+' update succe ed to '+ParamStr(2))
  else
  Writeln('Opacity update failed');
  except
  Writeln('parameter error');
  end;
end.
http://blog.csdn.net/redbirdli/archive/2007/02/15/1510602.a x