So when I boot up the game, it throws up an error message saying there's no disk in the drive. Each asks me to "Try Again/Cancel/Continue"; whatever I do, I get a second error message - same thing, slightly different path - and then the game boots.

Yes, that should be the important part, but the error messages are worrisome. How exactly can I stop them from displaying?

I've never had this problem, but since before I upgraded from XP, I had to resort to using a no-CD crack, as one of my discs was lost and the other...well, damaged, by a friend. Heh. So, maybe you could use this and eliminate the problem altogether? Honestly, I don't even know if this will work on GOG's copy of the game, but it might be worth a try. Sorry I can't help more.

same problem here

Hmmm, I never had that problem with my original version of the game. But there could be an easy solution to this. Locate and settings.ini file in your EG folder and take a look at it. If there is a line that states the location of the CD-ROM device try and change it to a location of the folder where you installed the game.

BACKUP your .ini files before you do this ofc.

Don't get your hopes up, because this is a bit of a wild shot in the dark on my behalf. I haven't played the game in years but I remember using a lot of mods and changes that were made through the modifications of the .ini files.

I'm having trouble too. Just installed says no disk. ?

I'm also seeing the same problem when I try to launch the game. It pops up a message box complaining that there's no disk in the E: drive. Canceling the message allows it to launch.

This didn't happen when I was using the game on Windows 8. I just downgraded my machine to WIndows 7 and reinstalled the game, and this started happening.

ColdZer0's suggestion didn't pan out. There is a config file in the game directory, but there's no setting that relates to the optical drive location as far as I can see. It looks as if the executable is trying find the CD so it can perform a CD check.

Running into this too with an unmodified fresh download from GOG. Game works, as everyone else mentions, but still get this disc check message. Mildly bothersome.