php 4.3.10 Zend version, and apache errors

Greetings.

I am getting some Arithmetic Exception exit signal messages in my
apache logs and intermittent lost pages in a photopost app, dating from
an upgrade to php 4.3.10, and I'm investigating whether this could have
anything to do with the Zend incompatability that is mentioned in red
on php.net for the 4.3.10 download.

php 4.3.10 comes with Zend, and the version mentioned both in phpinfo
and in zend.h file in the php distribution is v1.3.0. But the php
download page says we MUST have the latest version of the Optimizer,
which turns out to be 2.5.7. But, the Zend site doesn't cover our
Tru64 platform so I'm confused as to what I should do. Am I supposed
to separately install Zend? The php readme doesn't say so.

Is there a way to turn Zend off so I can see if that's where my error
is coming from? I couldn't find anything in php.ini.

Thanks heaps,
Ann Cantelow