I had a heck of a time removing the cover, following the directions in the iPod link instructions, pushing and prying at the clip from behind after removing the glove box.
It turns out there's an easy way:
1. Remove the screw (duh).
2. Insert a popsicle stick or similar gentle tool between the parts at the screw position.
3. Slide the tool to a point slightly right of center of the vent knob.
4. Lift the free end of the tool up to pry the right clip down and out.
5. Pull the left side down to release the left clip.
EDIT: For completeness, here's the plug to remove:
