Оформил: DeeCo
Автор: http://www.swissdelphicenter.ch

 uses
   ShellAPI, Registry;

 procedure OpenURL(Url: string);
 var
   ts: string;
 begin
   with TRegistry.Create do
     try
       rootkey := HKEY_CLASSES_ROOT;
       OpenKey('\htmlfile\shell\open\command', False);
       try
         ts := ReadString('');
       except
         ts := '';
       end;
       CloseKey;
     finally
       Free;
     end;
   if ts = '' then Exit;
   // remove quotes and commandline parameters 
  ts := Copy(ts, Pos('"', ts) + 1, Length(ts));
   ts := Copy(ts, 1, Pos('"', ts) - 1);
   ShellExecute(0, 'open', PChar(ts), PChar(url), nil, SW_SHOW);
 end;

 procedure TForm1.Button1Click(Sender: TObject);
 begin
   OpenURL('http://www.SwissDelphiCenter.ch');
 end;