Better stay with PHP 4 if PHP5 is not really required. PHP4 is faster.
What you need is to setup a opcode cache like APC.
APC binary for php 4.4.4 is available under lsws/lib/ directory.
You can modify the php.ini showed in the phpinfo page to load the APC extension.
The APC related error message probably is what happened before installing those Zend extensions. Not important.