Since you are in the script directory, there is no need to use the full filename including its directory:
Code:
ereader2html.py Firefly_60646.pdb Firefly_60646 "RJ Thomas" xxxxxxxx
I think you are missing the ".pdb" on the first argument and also it is a good idea to create a new subdirectory for each ebook (the 2nd argument, which does not have to exist yet).
EDIT: I suggest making use of "tab completion". Type a few letters of the filename (e.g. Fir) and then the tab key. The filename will be added by the command interpreter. I then do the same thing again for the directory (e.g. Fir) and delete the ".pdb" before adding the last two arguments (with a paste from the clipboard).