Microsoft Access Primary Key?

well, im workin on an assignment in college, and i have to set up a database system in access...but ive forgotten how to make my primary key have a prefix...

for example

istead of the auto number being "0001"

i would like it to say "MB-01"

how do i go about this?

I don't believe you can do that with autonumber, unless Access post 2K has that as a setting in options. You'd have to add the key manually.