I _ALMOST_ gave up, but I finally managed :)
In case anybody encounters the same problems, some hints:
1) make sure that if the SSD is connected before bootup, you start MS Dos and run maindiag.exe, you see the three lines with model, serial and firmware. otherwhise your mainboard does not recognize your SSD and you cannot flash. change SATA port or computer.
1b) make sure your mainboard DOES NOT reboot when disconnecting the SSD while in maindiag.exe!!!! as stated someplace else this could ruin your SSD.
2) If you see the three lines and everything seems to work fine but the firmware is not updated, use an Intel board (or a different board if you already try on intel)!
I spend about 2 hours trying every possible way flashing the SSD with an AMD board of a HP compaq dc5750 (where I saw the three lines and I got sucess messages ), but after every reboot, the firmware stayed the same. I then tried on an Intel i5 Dell Optiplex 980 and it took me 5 minutes to flash ...
The difference between the AMD and Intel board was that with the Intel board I had to wait a couple of seconds after I pressed a key when it said "press any key to continue". So probably with the AMD Board nothing got flashed so maindiag didn't re-examine the SSD while with the Intel board the SSD was flashed so maindiag.exe had to re-examine the disk.
3) roughly I followed: http://www.ullright.org/ullWiki/show/lenovo-thinkpad-t400s-samsung-ssd-trim-enablement
but in fact I didn't start maindiag twice but I did 2,1,4 only once. these are the exact steps:
a) connect SSD with a microSATA adapter to desktop computer, boot to dos from USB, start maindiag.exe, you see the three lines
b) power cycle SSD (from the microSATA adapter disconnect only the power cable for 1 second and reconnect it again)
c) choose option 2, you get sucesss, return to main menu of maindiag.exe
d) power cycle SSD (see b))
e) choose option 1, you get sucess, return to main menu of maindiag.exe
f) power cycle SSD (see b))
g) choose option 4, you get sucess,
h) power cycle SSD (see b))
i) return to main menu of maindiag.exe
j) quit maindiag.exe
k) reboot and check firmware with maindiag.exe --> SUCCESS!!!!
While I tried every possible way for 2 hours I never bricked my SSD - I think as long as you make sure you can power-cycle your SSD while connected and the computer does not reboot, you are quite save.