Thanks to Karl Dunkle Werner for writing up the origianl version of these steps.

  1. Download and install the PPDs. Check this page for the latest information:
    http://www.openprinting.org/printer/Ricoh/Ricoh-Aficio_MP_7503
    The direct downloads are here:
    Postscript:
    http://www.openprinting.org/ppd-o-matic.php?driver=Postscript-Ricoh&printer=Ricoh-Aficio_MP_7502&show=0.
    or pxlmono:
    http://www.openprinting.org/ppd-o-matic.php?driver=pxlmono-Ricoh&printer=Ricoh-Aficio_MP_7502&show=0.
  2. Go to the CUPS interface by pointing a web browser at http://localhost:631
  3. Click the Administration tab, then the Add Printer button.
  4. Choose AppSocket/HP JetDirect and continue.
  5. In the connection, write socket://arericohcopier.dyn.berkeley.edu
  6. Enter a Name, Description and Location that are meaningful to you.
  7. In the Or provide a PPD file section, click Browse and select the file you downloaded in step 1. Click Add Printer.
  8. In Options Installed, change the setting for
    1. Large Capacity Tray to Installed and
    2. Leave the rest as Not Installed.
    3. Click Set Default Options, at the bottom.
  9. Go back (using your browser's back button) and click General. Enter whatever settings you want.
    1. I changed Resolution to 1200 dpi,
    2. Duplex to Long Edge and
    3. Collate to On.
    4. Click Set Default Options, at the bottom.
  10. Go back and click Job Log.
    1. Change the JobType to Normal Print.
    2. Change the User Code to Custom UserCode. In the provided box, enter your ARE-provided print code.
    3. Click Set Default Options, at the bottom.
  11. Click the Printers tab at the top of the page.
    1. In the Maintenance drop-down, choose Print Test Page.
  12. On the command line, set the new printer as the default by typing lpoptions -d <printer_name>, (<printer_name> is whatever you provided as the name in step 6).

Known dependencies: definitely CUPS, possibly Foomatic (if your OS is kind of old).
You might also need the driver package from the OpenPrinting site (.deb or .rpm). I installed it, but it might not be necessary.

Best,
Karl