Using Manage | Security, you an only control access at the record level--not the field level.
You can either split the table into two or more tables linked by one to one relationships so that record level access works by limiting access to a single record that contains your fields to which you want to limit access, or you have to use techniques that limit access at the layout level.
What i ended up doing was using "conditional formatting" I set the formula: If Privilege Set = "Superintendent" the color of the text will be the same as the background. So the field looks blank.
We are going to upgrade to FMP11 Advanced in the next week or so. So i may be changing the way I do it.
Do you know if FMP 11 Advanced has a better way of dealing with access privileges?
You will find many new features in Advanced, but enhanced control of security settings will not be one of them--you'll have exactly the same capabilities.