In case anyone needs to connect CUPS with a Xerox WorkCentre PE120i or PE120 (which is actually the same thing without ethernet, I believe): You want to use the foomatic gdi ppd. If you're using Debian Etch, install foomatic-ppds and select the Samsung ML-200 (anything that uses the gdi driver is okay).
Took me three hours to find this. Adding it to the linuxprinting.org database gave me a whole lot of errors, so I'm simply adding it here. Announce it to others! (I hope you can find this through Google...)