Upon arrival at our hotel in Framingham, Mass, enroute to to Swedish Car Day 2012, we discovered we couldn't open the hatch! The key turned, and the power lock mechanism made the appropriate noise, but the external hatch release had no effect whatsoever. Luckily, this being a classic SAAB 900 hatchback, we were able to fold down the rear seat to crawl in for our suitcases. We greatly enjoyed Swedish Car Day in Brookline and hoped not to get a flat tire on the way home.
It's easiest if you crawl into the hatch on your stomach and release the latch with a screwdriver.
Once the hatch is open, it's simple to remove the upholstery screws with a quarter turn, then remove the trim from inside the hatch lid.
The upper edge of the trim panel is secured by snaps, just pull it off.
Thanks to Linnea Krajewski and Jonathan Williams for the tips that led to a resolution of this issue.