Controlling write access to a table

Hi.

I have a database with all of the particulars of our students and I am
adding a table that will contain all of the courses and the grades
attained by the students.

All this information is to be read by just about everybody, and the
bulk of the data will be written by several clerks, and, while we
wouldn't like just anybody altering these, we don't need terribly
stringent write security.

The marks (or grades) of the students are a different matter and we
want to restrict changes to this data to a very few people.

I'm presuming that this is not a unique problem, but I have been
unable to find anything helpful on google.

Can anyone assist me?

Would it be preferable to create a separate database for this information?

Regards,

Dave Coventry