Well I'm not going to tell you not to use auto_increment. I think it's the best way to create a unique id to use as the primary key of any table. When you use an auto_increment field you are guarenteed that you will have a unique id number for each record in that table, you can then use this number to link that record to anything else in the system because you know this number is unique to that record in that table.
I will however tell you to not limit your id field to be an int(4), that is just asking for trouble. Remember this little thing called the Y2K bug that scared the crap out of every one a couple of years back? This was caused because people wanted to save space and only store the last 2 digits of the year and not the whole 4 (or more not that we will live that long, but I bet there will be a scare on 9999 about the year 10000). So why limit the amount of stories that you can have to only 10000? You won't be eating up that much more space to make your id field int(9).
