I have a 2004 Dodge Dakota Quad Cab.

I'm looking at adding XM Radio to it, and I had some questions about
the factory stereo.  Specifically, I was trying to find out information
on what (if anything) the receiver can control.  The sales guy at the
place I went to (Car Toys in Dallas) said that it looks like it might
have the ability to just wire into the back, bypassing FM modulation.
The buttons on the bottom that say 1 & 5 also say Disc Up and Disc Dn,
so it appears there's some sort of stuff that can be hooked up to it.

Is there anywhere I can go to see what's on the back of the factory
stereo (which is AM/FM with cassette & CD).  Here's a picture of what
it looks like.  This isn't mine, I searched on the net, and found
this...

http://www.siegler.net/.pics/dodgestereo.jpg

Basically, I'm looking to find out some technical specs on the radio in
my truck.  Anyone know where I can find them?  Thanks.  I'm not really
looking to replace the factory radio, just add on to it.