PHP and MySQL, i bet this sounds very familiar for you. If you have a blog, a WordPress blog, a drupal, or a joomla website you will use both PHP and MySQL as the technology to serve your content management. PHP: Hypertext Preprocessor is a widely used, general-purpose scripting language that was originally designed for web development to produce dynamic web pages. An MySQL is a relational database management system (RDBMS)that runs as a server providing multi-user access to a number of databases.
PHP development began in 1994 and MySQL development began in 1994 too. After a while this 2 products are widely use together and along with Apache as the webserver. The final version of PHP 4 was released during August of 2008, followed by the final version of MySQL 4 on December of 2008. Both PHP 4 and MySQL 4 have been discontinued for almost two years. So the technology and security behind PHP 4 and MySQL 4 is far behind PHP 5 and MySQL 5.
WordPress already announce they will end their support for PHP 4 and MySQL 4. You can read their announcement on their blog post here. And as you know Drupal and Joomla already do the same thing this year too. From the WordPress data, now only 11% of WordPress blogs running under PHP 5.2. And they really clear state about their next release, that is WordPress 3.2 won’t support PHP 4 and MySQL 4 anymore. Thus WordPress 3.1 (will release at the late 2010) will the last WordPress that support PHP 4 and MySQL 4.
After this announcement i think PHP 4 and MySQL 4 will no longer use anymore. So are your hosting provider still use PHP 4 and MySQL 4? If so ask them to upgrade or move to another host.