Officially the Oki C5400 is not supported in CUPS. Fortunately thanks to Ewan McNabb I was able to set one up on a Linux server today. Oki provides a PPD file for download from their site but the HP LaserJet 4 driver works for testing purposes. Printing can be done through CUPS using IPP (ipp://printerip/ipp) and Windows clients can send data to the CUPS/Samba using Adobe's universal postscript printer driver.