New Database - Primary Key

Hello,

I've read a lot of the threads referencing Primary Key and I need a little
help. I'm creating a database for my company to track changes to channels.
This database will be accessed in different regions throughout the company
(possibly sometimes at the same time). I need to figure out how to create a
Primary Key for one of my tables. I've figure out how to use the DMax
function to increment #s, but if two users try to enter a new record at the
same exact time, one of them won't be able to save that record because the
one before got the #. I know this because its happened before.

Thanks.