Operation System MIPS needed

[Roberto Liarth <roberto.liarth@gmail.com>]

My friends,
 
First of all, congratulations for your best job. I am fan.
 
I am projecting a system. The project will run at PC, and operation system gonna be Linux. I would like to do a budget of MIPS. At this point one main information are necessary: 
 
How much MIPS the normal Operation Systems consume? Suppose minimum process running.
 
Can you help me?
 
Thanks in advanced.