"Tapping" into the existing speaker system...

Can anyone tell me if there is a way to tap into the existing speaker system in my 2000 Chevy Venture/Pontiac Montana to use with my portable DVD Player? I would like to use it in the same way Montanavision uses it. My vehicle did not come with that option but I have a Portable DVD Player that I hope I can adapt. Is there a connector that I can buy somewhere? Even if someone can tell me which wires to splice, I can even do it that way. Thanks.

The easiest/safest way would be to get an RF modulator that you plug the antenna into, then plug the modulator into the radio. You would then tune the radio into a unused frequency. There is also FM transmitter modulators that essentially create a mini radio station. No need to get behind the radio and it's portable, although the sound quality does suffer a little.