Have you mounted your CD as C: drive in DOSBox? What Horseman said is that you should mount your CD as D: (with the "-t cdrom" parameter), as well as a location in your hard drive as C:. You can mount more than one drive in DOSBox, and in this case you need to. Like for example:
Code:
mount c "c:\users\me\dos"
mount d "e:\" -t cdrom