Version 3 & 4

Hi, I'm wondering if PHP3 & PHP4 can co-exist ..... I've Php3 + Apache on a Win box and all works fine, but in order to try Php4 (the last release with patch) and Zend Optimizer, I've installed both on the same machine setting the right (well, probably not so right) parameters on httpd.conf of Apache server ........ The problem is that when I try to get a file that must be parsed by PHP4, nothing happen: I can't retrieve the page tout court .... (the page don't be download on my browser).... If I CTRL+SHIFT+DEL the system, seems the php.exe is hard freeze ..... Instead, the files that must be parsed by PHP3, work good .... Could anyone help me please? Many thanks in advance. max