Are you doing it in the directory that file is in? It's not smart enough to guess where the file you want to work with is located. That little ./ tells it to look for the file in the directory you're currently in (which is your Home folder by default).

Presumably that's not where you downloaded the flasher to, however, so you'll first need to change the directory you're in to the one the flasher's in with cd <directory>.

PPC or Intel, it doesn't matter. The flasher will run just fine under Rosetta on Intel.