1. As a start make sure the .htaccess file is correct. (see above) delete the whole line, save and upload. You may need to clear cache, history etc...

php.ini - you may or may not, need to use a default php.ini file. What your really interested in is the "register_globals on/off" this needs to be in both present and switched off.

create a file called phpinfo.php, and add the following code, to check your php config. upload to root directory and run.

<?php
// Display everything see more (this is the default)
phpinfo ();
?>

2. make sure you unzip and upload the package locally and then upload it. Dont just upload the zip and decompress. This can affect the chmod of the files (ones that you wont be modifying) :)

3. if you have any php files chmodded to 777 or 666 (see 2.), it will cause the "server error"
Hope this helps :)