Read my 60 Seconds Guide to DOSBox (and don't just read it - follow it too).

If that doesn't help, come back with details on how you mounted your C and D drives, how you did the install, how you configured sound, music etc.

DOSBox emulates MSCDEX, AFAIK. You could try to create an image of the CD, and mount it with the DOSBox "imgmount" command.

-t cdrom is enough, as explained in MiniMax's link stuff

I did everything as explained in Minimax's guide.
C: as the virtual harddrive ( mount c C:\dosgames\ )
D: as my virtual cdrom drive ( mount d J:\ -t cdrom ) I also tried -t cdrom usecd 0 -ioctl, but that did not work as well, may it be the original CD or an image of it mounted in Daemon Tools. I did not try the imgmount command yet, but i may give it a try.

I started the installation from the CD via install.bat, and just installed the game to C:\Crusade. I chose Soundblaster for Sound and also tried it without any device, but the problem still exists.

I already read in the intro for cdrom drives, that it would install MSCDEX ( although I don't know what it is ), so I'm confused, that Crusade is asking for it.

/edit: okay, just found the problem by chance. In the game dir, there's a file "game.cfg"

I found the entry
[VDFS]
*.VDF
$:\CRUSADE\*.VDF

and changed it to

C:\dosgames\CRUSADE\*.VDF

( copied the vdf files from the cd to the gamedir before )

Well, now it starts. Anyway, thank you for your efforts!