Every time i reflashed my phone i always used this site
http://wiki.maemo.org/Updating_the_tablet_firmware

when you pressed 0 and it gave you error stating kernel couldnt be loaded means that the only way is to reflash the kernel.

so

cd "%ProgramFiles%\maemo\flasher-3.5"
then
flasher-3.5.exe -F RX-51_2009SE_2.2009.51-1_PR_COMBINED_MR0_ARM.bin -f -R (remove -R if you want to flash the emmc as well as kernel)

the reason you remove -R is because, once you reflash the kernel and it turns the phone on. It wont be able to reformat the emmc. I don't know why but thats just how it is

then this to reflash the emmc
flasher-3.5.exe -F RX-51_2009SE_10.2010.13-2.VANILLA_PR_EMMC_MR0_ARM.bin -f

its not complicated but might be a new thing for you. It's easy and make sure you follow it properly.

and yes kernel is contained in the firmware.
In you case, you don't need to format the emmc. It should load maemo up just after flashing the kernel but it's up to you

emmc would erase every thing whereas kernel won't!