"Warning: ocilogon() [function.ocilogon]: OCIEnvInit() failed."or
"Unable to load dynamic library php_oci8.dll - Access is denied"
If the IIS is allowed to use the anonymous logon it uses IUSR_<machinename> account to read the files, therefore this user needs to have read access on oracle installation directory.
The SolutionGive it to them.
Install your Oracle client
The inet-user needs now access rights for the
IUSR_MACHINENAME needs read access to the _complete_ bin directory (be sure to check the "replace permissions" options when setting this).
You might want to use a dependency checker to verify exactly what access is needed.
Set these Environment Variables in Control Panel -> System -> Advanced -> Environment Variables
A posting by Andy Hassall says "IIS runs as a child of the IIS Admin service. This then runs as a child of SERVICES.EXE. Processes inherit environment from their parent. Since you can't really stop SERVICES.EXE without the system going tits up, changing the environment seen by IIS without a reboot appears tricky, as changing the environment for your command prompt or the system has no effect on other already-running processes."
Update: You may also be interested in my post on Using PHP OCI8 with 32-bit PHP on Windows 64-bit.
Update: There is a comment on how to set the PATH in IIS in this forum post