In this article, which was in fact written in January—February 2008 (well over two years ago), I explain what the benefit is of using a CDN and how the then-new CDN integration module 1.x for Drupal 5 could help you do that for a cheap FTP Push CDN.
This was in fact more of a proof of concept module and therefore this Drupal 5 version of the CDN integration module is no longer supported. This article has been published because it would otherwise only been gathering dust. It will give you a better view on Drupal’s history for supporting CDNs, i.e. how hacky this solution is in comparison with its follower, the CDN integration module for Drupal 6.