I have an 04 Dodge Ram with the factory radio and have an Aux Input for both my Sirius and Ipod. Not sure about your radio, but mine has the CD changer controls and that is what I plugged the Aux Input into on the back of the radio. Though the site is down right now, check out
http://dodgetruckworld.tenmagazines.com/ and go to the one of the "Audio" sub-forums there. I'm pretty sure that you can found out how to do it there.