Specifically this unit:
http://www.crutchfield.com/S-IMOD3ULiG3r/cgi-bin/ProdView.asp?g=186650&I=60744000

How easy? How was the sound quality?

...but if you installed it with an audio input adapter on the CD-C cable, or on the aux in of a DICe iPod adapter, you would have much better sound than if you used the internal FM mod (pfui!)

I tried HD in my last car on an Eclipse HU and it sounded very good - much better than FM.