run extension library as different uid/gid?

Hi, I have created an extension library for my own use. This library needs to access a storage area needs specific user ID to operate. If I start Apache as normal ( using User Apache, Group Apache in httpd.conf ), my PHP script fails to run. I try to setuid / setguid on the PHP script ( this script will call the function in my extension library ) to the specific uid/gid I need, it didn't work. The only way I can make it work is to run Apache as the uid/gid that I needed. But this is surely breaking something else. What should I do in order to resolve this? TIA. - Joe