Enabling MySQL with Windows Server 2003/IIS 6.0:
Find your php.ini file first, check phpinfo() to see where php is currently looking for php.ini. (i.e. Using the Windows installer for PHP 5.0.4, the php.ini file was placed in the C:\Windows dir.) I recommend, however, that you don't use the installer - go with full manual install.
Set the following in php.ini:
display_errors = on
error_reporting = E_ALL
This will make sure that you'll see any errors that arise during configuration. MAKE SURE TO CORRECT THESE WHEN YOU ARE DONE PLAYING WITH PHP.INI! Do not leave these settings like this on a production machine.
In php.ini set the following:
extension_dir = "pathtoextensions (ususally [yourpathtophp]\ext)"
extension=php_mysql.dll (make sure this is un-commented if its already in your php.ini)
In IIS, open Web Service Extensions, click "Add a new Web service extension..."
Type-in PHP for the extension name
Under required files:
Add [yourpathtophp]\php5isapi.dll
Add [yourpathtophp]\php5ts.dll
Click 'Apply' then click 'OK'
Create web sites like you normally would, but make sure they have executable permissions, not just script access. Under the "Home Directory" tab, click 'Configuration'. Scroll down the list at the top and see if you can find PHP. If you do, make sure the path to the executable for PHP is correct. If you don't find PHP in the list, click 'Add...', then browse to the correct executable, [yourpathtophp]\php5isapi.dll, and click OK. In the extension field, enter 'PHP'. Verbs should already be set to 'All verbs', leave it like that.
Create a test page with this code:
<? echo(phpinfo()); ?>
call it test.php, and place this file into the web site you just created. Browse to the page, with firefox preferably ;), and make sure that you have a MySql section with some MySql info in there. If not, then your paths are possibly screwed up, or you're still not editing the correct php.ini (again, look at the location that phpinfo() shows you, and just edit it there if you have to, then move it afterwards and re-config).
Hope this helps!