Try teleporting around the problem. I described the procedure here:

http://www.gog.com/forum/anvil_of_dawn/dark_lantern_catacombs_puzzle_help/post4

Cheers. I was guessing that yes, cheating might be a way around it, and I'm comfortable enough hex editing should it come to that.

Still a pain. Was tempted to LP the game but won't be able to if it's this unstable :(

I think it's only Dark Lantern that's the problem. There are some rolling boulders in other dungeons, but there aren't so numerous and are usually not at chokepoints.

No worries holmes, like everyone's been saying, Dark Lantern is the "toughest" dungeon in the game.

Tough because the game breaks, not because of difficulty? :D

Because of the difficulty spike.

If you go through the Underground City to the Elder Tree and then the Reed plains, there is a spell in the center that costs a lot of mana and will destroy boulders and traps.

Then you can go back and destroy the boulder to get the summoning horn.

If you have the seashell, you can go underwater and complete the sunken ship. The stone creature in the lantern guards the entrance to get to the book in the lantern, which will teach you a spell.

If you do the sunken ship before going into the Underground city, you should be strong enough to get through the reed plain to get the spell in the center.

Is there a way to make boulders move if they're not?

Sometimes if you're lucky, and at the risk of damage, you can just keep walking into a boulder over and over and sometimes it will move and start to roll/bounce like normal in the direction you pushed it.

If this doesn't work no matter how hard you try, you will have to either go back to an earlier save, use a save editor to teleport around it or hex edit the save file yourself.