I found the XM box. It is in the trunk on the drivers side, just behind the rear wheelwell. I installed a Neucleus NC-X2i iPod interface which plugs in-line with the factory XM radio. The unit works quite well although only "simple" mode works. I'm e-mailing the vendor to see if anything can be done to get the "advanced" mode to work. You can see the unit at: http://logjamelectronics.com/neucncx2i.html
I bought the unit and cable from http://www.sonicelectronix.com/
since they had it dramatically cheapter. I think I paid about $117 for the unit and the cable.
Hopefully this info will help others. I was suprised at how little info on iPod integration was on this site. Most other auto forums have dozens of threads on the subject.