This is more a bookmark for my reference than anything, but if you have a stock CentOS 5.x installation (maybe from a VPS image or a clean install on a dedicated box) you're going to have issues with Drupal 6.x.

It comes down to PHP version. It ships with PHP 5.1.6 and Drupal these days pretty much depends on PHP 5.2.x upwards to work. Utilities like Drush do too, so leaving PHP as it is, you'll find, is not really an option. To confirm you will have this problem, execute this command to check your PHP version:

Good news for all you people who want to process their own video on their Drupal website. While FFMpeg is a "forbidden" application as far as the Fedora project guys and gals are concerned (not sure why - usually because of some legal issue), the ATrpms repositories contain FFMpeg, the Linux command line video encoding tool you need to install to use the FlashVideo module:
http://atrpms.net/

Specifically, here is the Fedora 10 repository:
http://atrpms.net/dist/f10/