I used part of every method shown in this thread, Thanks for all your help and great tips friends.
UNIVERSAL DREAMUP V2009 PATCHED BY FORHIKE AND NATAS SOFTWARE
But I do not care too much, for I can telnet to it now, I have a root login, and I know about the linux kernel :-) And I made a copy of the software it came with, which I can write back to /dev/mtdblock/3 if I have to. Now it complains that the hardware could not be verified, on screen. Connected to that IP with a web browser, uploaded boot loader version 69, and voila, it boots again. A few tries later, and the dreambox clone successfully claimed the IP configured by DreamUP. Finally got tired of transferring files by floppy/cdrom, so I installed an old PCI network card, got the network going, and lo, DreamUP started working. I unearthed an old Pentium I in my garage, installed Windows 98 on it, built a null-modem cable from an old modem cable, and immediately got the error: '' is not a valid integer. This is, strictly speaking, a bug in DreamUP. The box that you run DreamUP on MUST have a working network connection. Alright, in case someone else passes this way and needs a solution.