PHP/MySQL: Auto Increment

Hi, I am creating a simple database to store course information. Each course is to have a unique primary key. I generate this key using the auto increment feature in MySQL. When I create a table, and add a bunch of rows, I get something like this: ID -- 1 2 3 4 Once I delete a few rows, the database might look like this. ID -- 1 4 And after I add a few more, it may look like this: ID -- 1 4 5 6 So, after a while the ID field has numbers that go all over the place. To get around this problem, I run a php routine that resets all of the primary key ids from 1 to whatever. I am worried that if there is more than one user accessing the database, the data could get mixed up. Is there a better way to keep this organized? Thank you, Beau