function GetPart(ABegin, AEnd, Str: String): String;
var
  b, c: Integer;
begin
  if ABegin <> '' then
    b := pos(ABegin, Str) + length(ABegin)
  else
    b := 1;
  if AEnd <> '' then
    c := pos(AEnd, Str) - b
  else
    c := length(Str) - b + 1;
  Result := copy(Str, b , c);
end;

function ButtonClick(Sender: TObject): integer;
var
  AStrings: TStringList;

  function FindText: String;
  var
    i: Integer;
    s: String;
  begin
    for i := 0 to AStrings.Count - 1 do
      if pos('Сейчас на форуме </a>: ', AStrings[i]) > 0 then
      begin
        s := AStrings[i];
        Result := GetPart('Сейчас на форуме </a>: ', ' (', s);
      end;
  end;

begin
  AStrings := TStringList.Create;
  Result := 0;
  try
    URLDownloadToFile(nil, 'http://forum.antichat.ru/', 'temp_file.txt', 0, nil);
    AStrings.LoadFromFile('temp_file.txt');
    Result := StrToInt(FindText);
    DeleteFile('temp_file.txt');
  finally
    AStrings.Free;
  end;
end;