function GetWindowsFolder:string;
{©Drkb v.3(2007): <a href="http://www.drkb.ru" title="www.drkb.ru">www.drkb.ru</a>,
 ®Vit (Vitaly Nevzorov) - nevzorov@yahoo.com}
var p:PChar;
begin
 GetMem(p, MAX_PATH);
 result:='';
 if GetWindowsDirectory(p, MAX_PATH)>0 then
  result:=string(p);
 FreeMem(p);
end;

public
 { Public declarations }
 Windir: string;
 WindirP: PChar;
 Res: Cardinal;
procedure TForm1.Button1Click(Sender: TObject);
begin
 WinDirP := StrAlloc(MAX_PATH);
 Res := GetWindowsDirectory(WinDirP, MAX_PATH);
 if Res > 0 then
  WinDir := StrPas(WinDirP);
 Label1.Caption := WinDir;
end;