first, thanks for helping me and all the info you supply.
second, thanks for relaxing me... well, i guess you know what is the feeling when your phone stops functioning and you don't know what's going to be with your data.

i was able to do a backup before installing that broken update.
i've also copied right now all the info appear in my Nokia N900 when i see it on my computer in mass storage mode.

can i do more (regarding backup etc)?

now for the flashing stuff - i have the following status:
I entered the command in the cmd like the following and nothing happened. This is what I got:

D:\Program Files\maemo\flasher-3.5>flasher-3.5.exe -F RX-51_2009SE_10.2010.19-1_PR_COMBINED_MR0_ARM.bin -f -R
flasher v2.5.2 (Sep 24 2009)

SW version in image: RX-51_2009SE_10.2010.19-1_PR_MR0
Image 'kernel', size 1705 kB
Version 2.6.28-20101501+0m5
Image 'rootfs', size 173568 kB
Version RX-51_2009SE_10.2010.19-1_PR_MR0
FIASCO subimage data length mismatch

and the N900 is in flash mode (can see the usb icon on the upper right corner).