Well, time for some follow-up, methinks!
Thanks to all for your helpful posts and advice. After much experimentation, installing, uninstalling, waving of dead chickens over the computer and so forth, it seems that the problem is limited to a certain set of .lit files. I'm thinking that perhaps these files have all been encoded by the same person (we're talking non-DRM here-I won't have that filthy stuff on my computer). So I've devised a series of cunning workarounds, and all is well in the Finch household once more.
Now, I've just got to organise the financing for that Sony Reader. Anyone interested in buying a 1980 VC Holden Commodore sedan?