Install problem WordPress2.8.4 on PHP5

I am using WordPress2.8.4.

I am using a rental server to host my WordPress website.
PHP on my server is changeable from 4 to 5 or from 5 to 4 by one click of a button on the control panel.

Recently, I changed php on my server from 4 to5. Then my WordPress become unstable.

The first time I changed from php 4 to php5, my web site got blank though the control panel was fine. Therefore, I erased database and files from server. Then, I tried installing WordPress2.8.4 again on PHP5, but I was not able to login to WordPress after the install (though I was able to install the WordPress). Because, after entering userID (admin) and password and push Login button, the website got blank.

I searched on internet and I found that comment out Line 337of “wordpress/wp-includes/canonical.php” is a solution.
Line 337 : add_action(’template_redirect’,’redirect_canonical’);

After erasing the line above, my WordPress behave right on php5 only “after” installing it.
But I still can not install WordPress on PHP5 because of the problem I mentioned (Because, after entering userID (admin) and password and push Login button, the website got blank.).

Currently, When I install WordPress, I have to use PHP4. Then, after installing it, I change PHP4 to PHP5 by clicking the button on the control panel of my server.

Does anybody know which code I should change to install WordPress2.8.4 with PHP5?
For some reason, I have to use WordPress2.8.4 little longer without upgrading it.

By the way, I tried with WordPress2.9.1. But the result was the same. On my server, I failed to install WordPress2.9.1. on PHP5.

OS: Linux
Web server: Apache2
php4 or 5
MySQL4.1