I looked on Red Hat Network... and found the following:
php-mysql-4.3.2-14.ent Red Hat Enterprise Linux AS (v. 3 for x86)
php-mysql-4.3.2-11.1.ent Red Hat Enterprise Linux AS (v. 3 for x86)
php-mysql-4.3.2-11.ent Red Hat Enterprise Linux AS (v. 3 for x86)
php-mysql-4.3.2-8.ent Red Hat Enterprise Linux AS (v. 3 for x86)
If you installed Apache and PHP (and php-mysql)) out of the box, it should work farily well. One problem that some people have is that the mysql-server package is not on the CDs and you have to register your system to RHN and subscribe it to the extras channel. If you have a redhat.com login, you should be able to access Red Hat Knowledgebase and find some answers to some additional questions:
Where are the MySQL and PostgreSQL server packages for Red Hat Enterprise Linux version 3?
If you use up2date to update your package, ie
it should resolve dependencies for you. If your subscription is current with RHN, then you might as well use it, your paying for updates form RHN.
If you have a specific error message or if you can elaborate a little more on the errors that you are getting or what you are trying to accomplish, I 'd like to help if I could. Post any errors.