You can buy adapters specifically for that through Marv Golden Pilot Supplies...or Aircraft Spruce. You could use a basic splitter from radio shack, but if you want to play it safe and not do damage to the aircraft's intercom, I would buy one from a catalog. I purchased one from Marv Golden, and record audio on a Sony personal digital recorder. It splits off the headset...not the mic...that way you can hear everything. I have a few videos on my youtube channel (link below) if you want to hear some samples of it mixed in with the video. Hope this helps. Good luck with the lessons!
www.youtube.com/909kick