Nice work. Here's a few suggestions:
1. Use database connection pooling
2. Separate business logic from presentation logic.
3. On deletion of some of the items, I noticed that the values became "null" and not really deleted entirely.
4. Work with a specific database system and encapsulate as much functionality as you can within it. It would be nice to see a good web front end for MySQL.
5. Like you pointed out before, error handling. Log all errors to a file so you can trace the errors.
Other than that, looks good
[This message has been edited by Rehan Malik (edited November 17, 2001).]