No problem! You are exactly right on the approaches. You are also right on the 396. It has to be a panel mount (read: mounted by an avionics tech...) gps to be certified for IFR use.
There are three components to an ILS: Guidance (vertical and horizontal), range, and visual (approach lights). Range information can be provided by any of several things: Marker beacons (only the OM is required for Cat I), DME, LOM, or crossing radials. So, the range equipment you need depends on the ILS approaches around you. He will most likely need a separate marker beacon antenna and receiver, as marker beacons operate on a different frequency than localizers. To make this a viable IFR aircraft I would recommend this and DME or an IFR certified GPS.
Your student/aircraft owner may want to do a price analysis on renting versus what it will cost to make his airplane into a viable IFR aircraft. (Note, while a top of the line Garmin panel is nice, he may be able to get some used equipment that works just as well.)
I'm on the road, so I don't have chapter and verse on all this, but the AIM has a lot of good information on instruments approaches and equipment. I think the ILS stuff is somewhere around 1-3-xx