Hi Ahwini,
HCM is not a pre-requisite for PPM implementation.
Without HCM integration, you will not be able to achieve the time booking functionality of resources in CAT2 timesheet and there by no actuals will flow from ECC system into PPM system.
Can you explain in detail on how you want to use PPM ?
Configuration Guide is available via note 1411953 as PDF attachment.
Help.sap.com link is SAP Portfolio and Project Management 5.0 – SAP Help Portal Page.
Best Regards,
Priyatham