on my macbook running tiger my n810 has to be off and not on a charger before i flashed
the steps i took were download image (duh) open up the 770 flasher , drag the image to the flasher wait until it says something like nothing attached and then attach the n810 to the usb and turn it on. like magic it flashes...

on the command line in tiger similar instructions- there is a command line instruction in the monster thread in the news category

i would assume on a linux box similar

in windows- i do not have a clue