The transaction code for this is MD51 - MRP Project. You could schedule this program in the background to automatically run MRP.
Here is a link in the help that could be of use:
Basically, from the linked help text:
"Via the allocation of material components to network activities, you determine the assemblies and raw materials that must be reserved or ordered for a project and trigger procurement via MRP or purchasing."
"Inventory management is envisaged for the SAP standard item category L (stock item). Depending on the settings in the material master and the bill of material, or the settings and assignments in the project system, the system generates for components with this item category a reservation or a reservation and a purchase requisition. For more information, see Procurement Settings.
If during procurement via MRP, the requirements canot be covered from stock, MRP decides whether the material is produced internally or procured externally. The system then generates as a procurement element either a planned order or a purchase requisition.
If materials have a long lead time (production time or delivery time), you can generate preliminary purchase rquisitions or planned independent requirements. For information about the prerequisites and settings necessary for this, see Advance Procurement."
Hope this helps.
Edited by: Paul Shrewsbury on May 5, 2009 2:31 PM