One good place to start is with the Frequently Asked Questions file from the comp.lang.PostScript newsgroup or the comp.sources.PostScript newsgroup. Note that in 'news-speak' Display Postscript is often abreviated to DPS.
Answers to Frequently Asked Questions on PostScript (and there is a little bit on Display Postscript) can be found in the FAQ
Bibliography on PostScript gives references to information on PostScript and Display PostScript