How do I set a process to use a certain processor?

A. This is called processor affinity where you set a process to use a specific processor on a multi-processor system.

Start Task Manager (Right click on the task bar and select Task Manager)
Click the Processes tab
Right click on the program and select "Set Affinity"
You can check the processors you want the program to run on (uncheck the ones you don't want it to use)

You cannot set affinity for a service, or set affinity for a program which has not yet been started.