First off, this is one of the best eggs of all time. I found this secret last night as well. Just to clear something up for a lot of people that may be confused, I'm pretty sure the "computer" is not actually running dos. It looks like some kind of modified unix kernel. The reason I believe this is that unix commands like "ls" also work on the machine.
On a side note - people that own the game may have noticed that there is also an "encode" and "decode" command available (I couldn't imagine a programmer adding these for no reason). I was up all night trying to figure out if these were related to some other sort of egg, but gave up after a couple of hours. You may also have noticed that there is an "rlogin" command that allows you to log in as other users within the "home" directory (with a password of course). Any ideas?