A System Center Operations Manager 2007 installation will result in lots of service accounts for running various management packs and performing various tasks. However a base install will require you to create 5 main accounts. These accounts will be explained below:
The action account is used by the management servers working with the clients. It gathers information and performs various tasks on agents.
Runas accounts are used to allow you to perform actions on clients from the management server with elevated privilages. Used for when your action account doesn't have privilages to perfrom a task so it uses the runas account to do this instead.
SDK and Config
Runs the SDK and Configuration SCOM services.
Data Warehouse Write
Used from a reporting server to write to the data warehouse SQL server.
For reading information from SQL.