Do you guys know any script which can replace phpmyadmin? I am facing some bugs with that script, and got fed up. Hoping to get some replacement to satisfy my clients.

Thank you in advance.

Since you have PHP4 installed you might want to try MyPHPAdmin:

http://wmf.dyndns.org/

How do they authenticate users and check that the users have access to which databases?

I saw the .htaccess and .htpasswd , I think they are just for authenticating users and let them log in the control panel, but can it check for users' access as well?