@Tim Hughes Hi Tim,
This is probably a bit late, however if understanding the data model underpinning your Peoplesoft system is required please let me know.
We have a software tool (Safyr) which extracts the metadata from the Peoplesoft data dictionary tables and lets you navigate, search and analyse to give you greater insight into how your system is set up from a data point of view. It also includes any customisations you have made.
Let me know if you need any additional information.