Hi sk,
the short answer is: probably yes, but it depends.
what do you mean be expenses related to manpower and what do you mean by forecast?
PCP supports forcasts incl. (with some tweaking) rolling forcasts as well as planning (incl. headcount) of personnel cost based on master data, payroll results, OM, TEM/LSO, compensation management. See here for an overview and here for an SCN document leading to 3 videos showing the most important process steps..
The details it can go into out of the box are a bit constraint, but still work for some. Most customers I've seen required more or less porgramming in the extensive BAdIs available.
just a quick shot - anything more would require a clearer understanding of requirements
kind regards
Sven