Trying to install either drupal 7.0-alpha6 or 7.x-dev resulted in the following message when I'd run install.php:
Parse error: syntax error, unexpected '{' in .../includes/install.core.inc on line 74
The error log displayed the same message.
The suggestions I found such as editing htaccess and liberal file permissions did not fix it.
My shared server used cPanel X, and that is where I found my solution. In cPanel, the PHP Configuration was set as:
The ".php" file extension will be processed by [System Default]
I changed it to [PHP 5].