function HexToInt(const Value: String): Integer;
 begin
   Result := StrToInt('$' + Value);
 end;

     Label1.Caption:=IntToStr( HexToInt('FF') );

 function HextoInt(HexStr:string):integer;
 CONST Hex : array['A'..'F'] of integer = (10,11,12,13,14,15);
 var
     i   : integer;
 begin
   Result:=0;
   for i := 1 to Length(HexStr) do
     if HexStr[i] < 'A' then Result := Result * 16 + Ord(HexStr[i]) - 48
                        else Result := Result * 16 + Hex[HexStr[i]];
 end;