Okay, a further look shows that turning off OpenGL hardware acceleration allows me to open this file and the atmosphere editor. I've got the latest drivers but the video card is a bit elderly - it's an nVidia GeForce 6600. Works fine for other things such as Poser 7 and C4D, though.

I'd value opinions on whether a newer card might help with this - and if so, what's a reasonable (i.e. reasonably-priced) nVidia card to buy? But I'm reluctant to throw money at the problem if it won't help!

Steve