Capture city, state and zip from zipcode table

[xg]

I have a zipcode table with all the zip code, city and state records. I
have a table called Student. I want to set up a form that:

If student's zip code is non-blank, zip field from zipcode table is dimmed
(unavailable).

If student's zip code is blank, user enters zip in a field, it will copy
city, state
and zip into student table from zipcode table.

How do I code that? I have limited knowledge of VBA.

Should I set one to many relationship for these two tables?

Thanks