I had this issue on a real Pentium 200 MMX in DOS Mode too.

Why don't you just mount c:\ ?

mount c:\ as c:?

I think the problem is that the installation program from the CDROM checked how much free space does the Z drive has, which is zero of course... The C: had 870mb of free space as I have set it.

Can we have a copy of your mount commands, and how you start the installer?

here is the command:

dosbox -c "mount c c:\wb\games\ -size 4025,127,16513,1700" -c
"mount d e:\ -t cdrom"

where e: is my physical cdrom with cd in it.

and once i am inside the box,

i need to do first

set temp=c:\

so that the game installer doesn't complaint about having zero virtual memory

then i run the game installer at

d:
install.exe

when i do the install, it say i got zero byte of free disk space

I have never used the -size option - would it be possible for you to use something like -freesize 900?

Also, try doing a mkdir c:\tmp and set temp=c:\tmp before you run the installer.

the -size and its parameters are copied from the readme.txt of dosbox. of course i tried using -freesize.

the mkdir tmp and set temp=c:\tmp doesn't work either