Resource Forecasting/Levelling Blues

[ChrisCreole]

I have inherited a plan that already has work (in hours), generic resources (based on skill sets), a required start date (for the whole project), and a required finished date (for the whole project). Is there a way which I can forecast the required number of resources for each role (generic resource)?

I tried raising the allocation percentage on the resource sheet as a means of producing this calculation but project will not shorten the duration (beyond what one individual could finish if fully allocated) for an individual task unless you increase the number of resources on that task or by increasing the allocation on an individual basis.

Any advice would be appreciated.