The parking brake must be fully released, and you may have to ratchet it back on the adjuster a few clicks to get the shoes below the groove in the little drum. The adjuster is accessable through one of the lug bolt holes, about 1:30 I think. Turn the rotor until you can see the star wheel, then stick a screwdriver or brake tool in there and turn it a bit. I don't remember which way, alas, but one way will tighten and the other loosen -- the direction will the be opposite on the other side.
The rotor can also stick to the hub -- a few taps with a steel hammer will usually break it loose.
You may have the original rotors on there, in which case I'd expect them to be rusted down pretty good.
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!