There is not a:\ in GNU/Linux.
It's /dev/fd0 and you'll have to mount the unit.
Put the diskette.
mount /dev/fd0 /floppy (make sure you have a directory called /floppy in
the base directory).
Then go to /floppy
If you can see there the file you've downloaded, go to /floppy and type
dpkg -i nethack_3.2.3-3.deb
-i is for "install".
If you change the diskette, umount it first (umount /dev/fd0).
If there are extra issues, I don't know. I'm pretty new at GNU/Linux, man.
It's the stuff I do when I install packages from the CD-ROM.
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