Welcome to the forums.

What is the reason in front office blog creation? A user will have to register anyway, so why can't he/she go to backoffice and create a blog?
If you're looking for an easy solution check the [url=http://forums.b2evolution.net//viewtopic.php?t=15842]Userblog plugin[/url].

Good luck

Thanks for your reply, though it's a bit late (I have already coded the plugin). My goal is to have a lightweight BO, with a minimum of functionnalities, because the website I am working on seems to have to much data for b2evolution BO to be efficient (for example, it is very very long to display the user list). The BO will be used only by the administrator, and normal bloggers will have to use the Front Office... Thanks for your link, it's a shame I did not know this plug-in before, I'll know for the next time...