unit Unit1;

interface

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, StdCtrls, ComCtrls,RichEdit,Shellapi;

type
  TForm1 = class(TForm)
    RichEdit1: TRichEdit;
    Button1: TButton;
    procedure FormCreate(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
    procedure Wndproc(var Message : TMessage); override;
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}

procedure TForm1.FormCreate(Sender: TObject);
var
 mask: Word;
begin
 mask := SendMessage(RichEdit1.Handle, EM_GETEVENTMASK, 0, 0);
 SendMessage(RichEdit1.Handle, EM_SETEVENTMASK, 0, mask or ENM_LINK);
 SendMessage(RichEdit1.Handle, EM_AUTOURLDETECT, Integer(True), 0);

 //Some text in RichEdit
 RichEdit1.Text := 'Scalabium Software'#13#10 +
   ' Site is located at www.scalabium.com. Welcome to our site.';
end;

procedure TForm1.WndProc(var Message: TMessage);
var
 p: TENLink;
 strURL: string;
begin
 if (Message.Msg = WM_NOTIFY) then
 begin
   if (PNMHDR(Message.lParam).code = EN_LINK) then
   begin
     p := TENLink(Pointer(TWMNotify(Message).NMHdr)^);
     if (p.Msg = WM_LBUTTONDOWN) then
     begin
       SendMessage(RichEdit1.Handle, EM_EXSETSEL, 0, Longint(@(p.chrg)));
       strURL := RichEdit1.SelText;
       ShellExecute(Handle, 'open', PChar(strURL), 0, 0, SW_SHOWNORMAL);
     end
   end
 end;
 inherited;
end;

end.

（出处：DelphiFans.com）