apparently foo2hiperc also works with the C3100. I used the C3200 PPD file, I don't really know the differences between C3100 and C3200, but it works well enough for a first try.
I had already given up on this printer, but now I dug it up once again, and only a lucky googling made me find this driver. It's unfortunate the printers that actually work well under linux are not listed in openprinting.org (foomatic?).
I added an entry for the C3100: http://openprinting.org/show_printer.cgi?recnum=Oki-C3100
Would it be a bad idea to add the other supported printers into the DB? I don't have those, but I can add some basic stubs about the others.
Thanks to Rick Richardson for the good work.