There is a file (PRINTER) in archive which should be copied to Mossys:Devs/Dosdrivers. It will mount PRINTER: device (not assign, just another device like PRT: PAR: SER: PS:) using included l/printer-handler. After that, programs can save their work (postscript files or image files) to PRINTER: device. PRINTER: and l/printer-handler will convert data to printer-specific stream and save it to file stored in environment variable PrinterOutput.

In an example

setenv save PrinterOutput NETPAR:

i set environment variable value to NETPAR: which is standard device created by geit's netprinter.device (should be mounted previously). This variable can store to simple file path like Ram:file etc. and then printing system will print to file. It should be typed once in shell. Refer to AmigaDos documentation.
It's ok to put my files to MOSSYS: this archive was prepared to use MOSSYS: and any copying files to other directory may cause troubles.

Regarding PPDs files:
I suggest checking HP subpage with drivers:
http://h20566.www2.hp.com/portal/site/hpsc/template.PAGE/public/psi/swdHome/?sp4ts.oid=81956&spf_p.tpst=swdMain&spf_p.prp_swdMain=wsrp-navigationalState%3DswEnvOID%253D2020%257CswLang%253D%257Caction%253DlistDriver

and download linux or earlier macosx drivers and get Postscript PPD file from that. I'll add simple postscript ppd file in next release. In printers prefs you select ppd file and click on Add button. PPD file will be converted to iff format and then You can change options + check Default printer.