program avalon 98 key with ecu

hi
i have 98 avalon xls and i have to change ecu so i bought a used ecu.I came to know that no body can program my old keys with this newly purchased ecu. I dont dont know what to do any body can help me that how i can program my keys with this ecu or i have to buy new keys and if i will then how i will be able to program new keys with this ecu. thnakyou