[poli-smen]

А так?:

Код:

procedure TForm1.Button1Click(Sender: TObject);
var
  f: string;
  k, p1, p2: Integer;
begin
  for k := 0 to Memo1.Lines.Count - 1 do
  begin
    f := Memo1.Lines[k];
    p1 := Pos(':', f);
    if p1 > 0 then
    begin
      Inc(p1);
      p2 := PosEx(';', f, p1);
      if p2 > 0 then Memo2.Lines.Add(Copy(f, p1, p2 - p1));
    end;
  end;
end;