在windows2000下增加了一些API,可以轻易的实现半透明的窗体，源程序如下，必要的地方我加上了注释

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，其他的我不太清楚，因为没有api帮助

end;

end.