Microprose tried to be clever in using BIOS calls to detect which disk is present in the floppy drive. However, the information that
install.exe is looking for gets lost somewhere in the many filesystem layers between it and the actual disk. This is not a problem unique to emulation; CD-ROM-based installation sometimes had trouble, as did some not-quite-IBM-compatible PCs.
There are two ways to work around this:
First, you can make images of the disks, and mount those images in DosBox. You'll need to specify the disk geometry when mounting the image:
imgmount -size 512,18,2,80 a: /path/to/your/disk/image
This is not the recommended method, as there's no easy way to switch out disk images during the installation process.
Second, you can bypass the installer entirely: the
mpscopy.exe utility on the first disk does the actual work of installation, and all it cares about is that the files it's looking for are present. You can copy the files from all three floppies into a single directory somewhere (the easy way) or switch out the floppies as-needed (the harder way). Run it directly:
mpscopy -c a: c:\colonize
If you're switching out floppies, you may need to use CTRL+F4 to inform DosBox that you've done so. Once the files are copied, run the configuration program to set up sound:
mpscopy.exe and the floppy-detection issues are not unique to Colonization; the issue and its fixes may also apply to other DOS-based Microprose games.