SALVATION:

my attempts at following http://www.orient-lodge.com/node/4254
were frustrated by the flashed program halting with a non recognition comment:
Suitable USB device not found, waiting
I looked for advice about using the sd card to feed an OS to my N900. In this context I came across
"comment 1"
https://bugs.maemo.org/show_bug.cgi?id=11306#c1
who talked of CHARGING THE BATTERY.
My N900 ONLY SEEMED with its yellow LED to be charging, and to be "charged".
A German source mentioned that THIS WAS FAKE if there was no OS of the N900 supporting a necessary sub-OS.
After buying a DT-33 I charged the BJ-5 and finally
IT FLASHED! (following http://talk.maemo.org/archive/index.php/t-35440.html)

sudo /usr/bin/flasher-3.5 -F /home/go/Downloads/RX-51_2009SE_3.2010.02-8_PR_COMBINED_MR0_ARM.bin -f -R

1.first start the flasher, it'll say device not found,
2.turn the phone completely off, don't turn it on, and
3.only after you've started the flasher,
4.connect the USB cable with the phone,
5.don't turn it on, press U?...

It'll flash...(w/o pressing u) ((&w/o SIM-card)