in car dvd player

Hi,I recently jus purchased a dvd player for the car and the guy at the shop told me i needed a fm modulator.I want to replace the stock cassete player in the car with a dvd player.Do i need a fm modulator? And can sumone give me a link or tell me the basics of wiring the dvd player.

Thanks

Is it THIS ONE?  If so, you cannot simply replace your in-dash unit with this since it is only a player and does not have an amp or pre-amp.  That's why there's no volume control, it is intended to simply be a source deck and it requires a control unit.  You need to run this through a head unit or pre-amp.  And even if you did buy the FM modulator it would do you no good unless you had a head unit to receive the FM signal.  This is an add-on unit to a head unit.  THEN you either need the FM modulator to send the signal to the head, OR (the far better solution) you need a head unit with an auxiliary input, either RCA or digital (preferred.)

Whoever is telling you that this player with an FM modulator can replace your head unit is simply wrong.