Difference between mysql4 and mysql5 

MySQL 5 introduced new important features
1. Cursors
2. Triggers
3. Stored Procedures
4. Views



after  importing all the data from MySQL4 to MySQL5, it's very important to run:
mysql_upgrade

please check below link to view complete details:
http://dev.mysql.com/doc/refman/5.0/en/development-history.html