When I try to run the install I get an Internal Server Error. I notice that if I comment out these two lines in the .htaccess file
php_value display_errors 0
php_flag register_globals off
I can proceed to Safe mode restriction errors, which I will take up with my sysadmin after I figure out what to do about the Internal Server Error.
Your sysadmin should probably be able to address this too.
For most users and setups, those lines are fine, but some PHP and Apache configurations don't work well (or at all) with them.
You can safely remove them from your .htaccess if you need to (the
display_errors one is there to make it easier for people to enable errors when they're having problems, and the
register_globals one makes sure an old deprecated PHP feature is deactivated).
If you have a "local" php.ini you can change, you could make sure that it contains those same settings.