Over the last few days I've helped the boss go over some of our web server stuff, and I've found a few things.
*. Our MySQL connectors were old: I found new ones.
*. Microsoft has a plugin for IIS to accelerate & cache PHP 5.2 & 5.3
*. If you try upgrading to PHP 5.3, some of your stuff may break because of updated password code for MySQL: one blogger posted a solution that is more or less "reset the password".
*. There's a developer that's been patching Wordpress to run with PHP's MySQLi driver.