I may be barking up the wrong tree, however, there were bugs in PHP 4.3.10 with the Zend Optimizer and TurkMMCache, which are fixed in later versions. You just never know what ISP is running what versions and why they haven't upgraded. See the link here for more info and more links:
All of you that are having problems report running PHP 4.3.10, so I am suspecting that this is the cause.
To find out if your installation is running Zend or Turck you will need to run a PHP info file.
I have attached a file called info.php which you can upload to your server and run like this: http://<yourserverURL>/info.php
Where yourserverURL is you website address.
To test this out, you would need to attempt an install with another more recent version of PHP. Maybe you can find a free ISP to attempt the install, or upgrade your PHP version.
The other approach that I would take is this:
1. delete everything except the download file, including all moodle database files and start over with a fresh install.
2. Run the install
3. Examine the web server log files for messages
4. This should give you a clue as to the location of the breaking code
5. Post that information here, so we can take a look at it.
Hope this helps,