[MOVED]

I think you need to install the game first (either from real floppies or from images).

You may need to use imgmount to mount images:

DOSBox readme wrote:

IMGMOUNT A utility to mount disk images and CD-ROM images in DOSBox. IMGMOUNT DRIVE [imagefile] -t [image_type] -fs [imag […]
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IMGMOUNT
A utility to mount disk images and CD-ROM images in DOSBox.

IMGMOUNT DRIVE [imagefile] -t [image_type] -fs [image_format]
-size [sectorsbytesize, sectorsperhead, heads, cylinders]

imagefile
Location of the image files to mount in DOSBox. The location can
be on a mounted drive inside DOSBox, or on your real disk. It is
possible to mount CD-ROM images (ISOs or CUE/BIN) as well, if you
need CD swapping capabilities specify all images in succession.
The CDs can be swapped with CTRL-F4 at any time.

-t
The following are valid image types:
floppy: Specifies a floppy image or images. DOSBox will automatically
identify the disk geometry ( 360K, 1.2MB, 720K, 1.44MB, etc).
iso: Specifies a CD-ROM iso image. The geometry is automatic and
set for this size. This can be an iso or a cue/bin.
hdd: Specifies a harddrive image. The proper CHS geometry
must be set for this to work.

-fs
The following are valid file system formats:
iso: Specifies the ISO 9660 CD-ROM format.
fat: Specifies that the image uses the FAT file system. DOSBox will attempt
to mount this image as a drive in DOSBox and make the files
available from inside DOSBox.
none: DOSBox will make no attempt to read the file system on the disk.
This is useful if you need to format it or if you want to boot
the disk using the BOOT command. When using the "none"
filesystem, you must specify the drive number (2 or 3,
where 2 = master, 3 = slave) rather than a drive letter.
For example, to mount a 70MB image as the slave drive device,
you would type:
"imgmount 3 d:\test.img -size 512,63,16,142 -fs none"
(without the quotes) Compare this with a mount to read the
drive in DOSBox, which would read as:
"imgmount e: d:\test.img -size 512,63,16,142"

-size
The Cylinders, Heads and Sectors specification of the drive.
Required to mount hard drive images.

An example how to mount CD-ROM images:
1a. mount c /tmp
1b. imgmount d c:\myiso.iso -t iso
or (which also works):
2. imgmount d /tmp/myiso.iso -t iso

So, you should mount your floppy images such as...

imgmount a c:\oldgames\rex\rex.a.ima -t floppy

(I don't know if you can't specify various images in the same line, and swap between them using CTRL-F4)

mount c C:\oldgames

A:
INSTALL.EXE (install to C: to whatever folder you want).

Thanks. I tried this, and here is the result. Does this give you a clue?

Next, I'm going to try going into the a: drive of my rex directory, see what happens, and I'll keep you posted.

Well...I finally made it to the Rex setup screen

and now it's asking for disk # 2; I tried pressing "ctrl + F4" , but setup says "wait. that's not disk 2. Try again." Anyone know how to switch floppy images in Dosbox? I'm stumped.

just now I tried to mount all 10 of the rex nebular floppy diskette images thus:

pressed <enter> but Dosbox said "image file not found." Is there any way to mount several floppy diskette image files as a group in DOSbox?

I tried this; no go. so I keep trying:

Now I'm really stumped. Is there a way to mount multiple floppy images from my oldgames\rex directory as a group?

Swap Disks in OS X

Some game install programs are flexible enough to let you copy all of the install files from the various floppies into one folder and then mount that folder as the A: drive and install from it. It works with the floppy version of Rex that I have.

Thanks for the link. I tried using that example, pressed <enter> but again, it didn't work for me. What am I doing wrong?

Now I'm going to try mounting my oldgames\rex directory as the a: drive...

I mounted it, pressed <enter> and this is the result. Really puzzled.

You have to copy the files out of the floppy images. IMGMOUNT each one in turn, and copy the files out into a folder. Or you can use a tool like WinImage to copy all the files into a folder outside of DOSBox. After all the files are copied out into a folder and that folder mounted as A: it should look like:

1Directory of A:\.
2.              <DIR>            19-12-2008 11:20
3..             <DIR>            19-12-2008 10:02
4INSTALL  EXE            100,993 14-09-1992 11:55
5MPSCOPY  EXE             31,267 14-09-1992 11:56
6MPSLABS  001          1,315,354 14-09-1992 11:57
7MPSLABS  002          1,457,533 14-09-1992 11:59
8MPSLABS  003          1,457,330 14-09-1992 12:03
9MPSLABS  004          1,457,664 14-09-1992 12:04
10MPSLABS  005          1,457,358 14-09-1992 12:07
11MPSLABS  006          1,457,360 14-09-1992 12:09
12MPSLABS  007          1,457,248 14-09-1992 12:12
13MPSLABS  008          1,457,485 14-09-1992 12:14
14MPSLABS  009            444,336 14-09-1992 12:15
15MPSLABS  IDX              5,598 14-09-1992 12:15
16README   TXT              2,638 14-09-1992 11:56
17   13 File(s)        12,102,164 Bytes.
18    2 Dir(s)          1,474,560 Bytes free.

I thought I did extract the contents of thse 10 Rex Nebular floppy images several months ago, but I guess I didn't. 😦
Well, I've just extracted them now into my oldgames\rex directory, ran the install program, but now it's asking for disk 1 and I have to press <enter>. I've already pressed <enter>, no go; pressed "ctrl + F4", no go; pressed "Fn + ctrl + F4" but still no go.

Pressing the keys and a: does nothing.
puzzled

exact set of files in that directory and mount points please.
(don't use -t floppy or do use it. Can make a large difference (for example turbo C 2.01 doesn't work with -t floppy if you copy files in one directory))

It doesn't seem to care about "-t floppy" on the A: drive mounting. Make sure that you have all the files in your folder that are shown in the directory listing I provided. The version number on the installer is the same one as mine, so this should work if you set it up correctly. 😉

My mounts:

and here's my set of rex nebular floppy diskette extracts:

Now that the files are out of the images, you don't need to mount the images.

mount a c:\oldgames\rex
a:
install

Of course you will also need to "mount c c:\oldgames" or some such to have a place to install to.

Thank you so much for your patience and your kind help, guys! 😁 I finally got the game installed. Here are the first couple of the intro screenshots:

The MPS labs screen

and the title screen

You can get the last patch and bonus disk from here. However, you should probably not use the bonus disk until you finish the game, since it could spoil stuff for you.