hi,
well, after some time, we found a solution. for all our printers (4100, 2300, 4650) we use the same ppd - the one for 2300. the setting of duplex and other things now work consistently.A bit a shot in the dark, but when I have problems with correct configuration via the web interface, I try to install the printer from the command line like lpadmin -p printer-name -v socket://ipaddress\ -P /atheneraid/tausch/Software/drucker/NRG-DSm415_PXL.ppd replace the last line with your ppd. This printer still won't accept mail, so I use the cups web interface to activate and configure the printer.
there is just one annoying issue - when printing some postscript files on 4100, it's printed reversed - i.e., white text on black rectangles :( it happens only with some of ps's... this happens whatever driver we use (hplip, hpijs) except for the postscript ppd, but then it's not possible to change duplex settings for the printer. there's probably some problem with ps fonts, but i cannot find anything relevant on web.
I can't find a ppd for that printer on linuxprinting.org.
sorry for confusion - it's 4650... best regards, -- Lubos _@_" http://www.lubos.vrbka.net