<?php
system("dir");
?>

This causes apache to hang until you kill the request handling process using the task manager; the script then completes and produces the output:

Warning: Unable to fork [dir] in i:/cms.wwwroot/test/test.php on line 2

The same effect is evident with exec and popen.
The backtick operator causes Apache to GPF.

If you use the CGI version, things work as expected.

The binaries are those from php4win.de (php4.0.4-win32-20001210).

This sounds like a deadlock -- there is that mutex for chdir in the exec/popen code - maybe it's related to that somehow? Or perhaps it's more of an issue with Apache itself.

If you need more info, just let me know.

--Wez.