转贴一篇千堆雪大侠的代码，确实好用！
在windows2000下：
unit Unit1;
interface
uses
Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms, Dialogs;
const
WS_EX_LAYERED = $80000;
AC_SRC_OVER = $0;
AC_SRC_ALPHA = $1;
AC_SRC_NO_PREMULT_ALPHA = $1;
AC_SRC_NO_ALPHA = $2;
AC_DST_NO_PREMULT_ALPHA = $10;
AC_DST_NO_ALPHA = $20;
LWA_COLORKEY = $1;
LWA_ALPHA = $2;
ULW_COLORKEY = $1
ULW_ALPHA = $2
ULW_OPAQUE = $4
//新增加的常量定义
type
TForm1 = class(TForm)
procedure FormCreate(Sender: TObject);
private
{ Private declarations }
public
{ Public declarations }
end;
function SetLayeredWindowAttributes(hwnd:HWND;
crKey:Longint;
bAlpha:byte;
dwFlags:longint ):longint;
stdcall;
external user32;//函数声明
var
Form1: TForm1;
implementation
{$R *.DFM}
procedure TForm1.FormCreate(Sender: TObject);
var l:longint;
begin
l:=getWindowLong(Handle, GWL_EXSTYLE);
l := l Or WS_EX_LAYERED;
SetWindowLong (handle, GWL_EXSTYLE, l);
SetLayeredWindowAttributes (handle, 0, 180, LWA_ALPHA);
//第二个参数是指定透明颜色
//第二个参数为0则使用第四个参数设置alpha值，从0到255
end;
end.
