Operations Manager 2007 Performance and Scalability

The official tool for performance and scalability planning will be System Center Capacity Planner (SCCP).
SCCP combines the best practices presented in this document along with performance modeling and simulation to build detailed sizing guidance specific to your environment

you can use this document which describes performance and scalability guidelines to consider when planning a Microsoft System Center Operations Manager 2007 deployment.

Operations Manager 2007 Performance and Scalability White Paper
http://download.microsoft.com/download/d/3/6/d3633fa3-ce15-4071-be51-5e036a36f965/OM2007_PerfScal.doc