To tell you the truth Dave, the drive letters were changed - by me, a while back, when I got my second hard drive added. I think I'm sensing a pattern here - I need to stop tinkering.
Anyway, after I reinstalled everything is when I got the new error. Before then, my fresh-from-the-shop computer kept acting like there was no CD in the tray at all ("please insert disk" - even though there was one).
So, I can now play the game normally, I just hate the way it tries to install FotR everytime I insert the CD. I just click it off and it's no big deal, but still irritating, and making me wonder if other things aren't working.
Oh, thought I should mention; when my comp first came back from the shop, there was an empty EF II folder on my C drive. I keep EF II, RS, and DG / DG-Vietnam on the D drive. Only West Front is on my C drive (I've been too lazy to move it). The EF II folder (the "real" one) was still on the D drive, filled with the usual info, but I couldn't play on it. Perhaps the guy at the store who worked on it got confused and assigned a dll entry to the C drive? I noticed that when I was reinstalling, the comp defaults to the C drive, but I overrode this manually.
Anyway, thanks again for the advice.