'Your PHP installation appears to be missing the MySQL which is required for WordPress.'

The problem is in the "wp-settings.php":

if ( !extension_loaded('mysql') )
die( 'Your PHP installation appears to be missing the MySQL which is required for WordPress.' );

So, this issue can be solved:

1. Make sure you have libapache2-mod-php4 installed;
2. Edit /etc/php4/apache2/php.ini, uncomment ";extension=mysql.so";
3. Restart Apache server;
4. Try to reload http://BlogServer/wp-admin/install.php in the browser, it is ok now!