Rob: I don't know how I missed your post. I thought I was keeping a good eye for any replies and somehow I missed your post. Hmmm... Anyway, thanks for trying. I truly appreciate that.
OK - I installed wine and xnview and this seems to work:
# Use temp file names from gimp, it reflects the user's choices in gimp.rc
# change as indicated if you always want to use the same temp file name
tempwinfile = "C:\\Windows\\Temp\\tempfile.png"
tempfilename = "/home/rob/.wine/dosdevices/c:/windows/temp/tempfile.png"
# !!! Note no run-mode first parameter, and user entered filename is empty string
pdb.gimp_progress_set_text ("Saving a copy")
pdb.file_png_save_defaults(tempimage, tempdrawable, tempfilename, tempfilename)
# Command line - Change to match where you installed XnView
command = "/usr/bin/wine \"C:\\Program Files\\XnView\\xnview.exe\" \"" + tempwinfile + "\""
args = shlex.split(command)
Just replace the bits of the previous version and change your home/rob/ path to yours.
This is necessary to overcome the wine/linux paths.