Audio Systems: upgrading cd player in 2001 Pontiac Montana, nightmare air, pontiac montana

Question
I would like to upgrade the stereo in my 2001 Pontiac Montana to something that will play CDs encoded in MP3. I called a local retailer/installer with a good reputation to ask approximately how much the installation would cost, and he advised me that, besides the deck and installation, I would need a "simulator module" because some of the vehicle's other computer functions (chimes, power windows or locks?) were included in the factory stereo. I have searched online to try and find other comments to verify this suggestion but come up with nothing. Does this sound credible to you? Any other concerns/suggestions regarding upgrading the deck in this vintage Montana?

Answer
you did call a good shop, and he is correct don't cut corners here buy the interface he is telling you to get  if you don't
your van is going to turn into a nightmare  air bag lights,no gas,or running out of gas when it tells you half tank no warnings  we use it all the time  to replace your radio we charge  $140.00 NO RADIO  
follow this link is for the adaptor

http://www.oemautosound.com/c-132-oem-integration-modules-interface.aspx