I do'n quit understand:
- you want to offer free blog scripts for your users
- you want to offer free blog instances for your users
In first case, I'd recommend using Fantastico DeLuxe
In the second case, a nice solution is Drupal CMS: after installation, each registered user may (can) get a free blog.
thanks for your answers! (gupi i want to offer free blog instances for my users). But i don't understand how can i provide a third level domain as yourname.blog.com that works with cpanel? have i to set unlimited subdomains?