I’ve been having similar problems. I’ve set up Apache and PHP 4.3 on my machine as well as a sufficiently current version of MySQL. My browser just tries to open wp-admin/install.php as a text file, and if I go to the CLI and type # php wp-admin/install.php I get a line telling me that “Your PHP installation appears to be missing the MySQL which is required for WordPress.” Aside from the bad grammar, it’s very confusing, because I could swear I’ve got MySQL running.
