Thanks a lot for the Rewrite tip. And sorry for calling it a bug :/
The thread I'm talking about is 69764. It was weird, I kind off got stuck out of my admin account. In the DB, my account wasn't blocked. I tried to follow the tutorial at thread 15508. But I just couldn't get in. And there were no errors shown. I might have misconfigured something. Who knows xD
I also would like to know whether there is a possibility to remove the .html from friendly URLs.
Thanks for the quick response !
Btw, Lucas, I am quite pleased that Open Geek replied this quickly

It's just that I got a little disturbed that no one was replying in two days and that I was stuck out of the admin account. Sorry 'bout that.
I will try to give something back (video tutorials, help on this forum, etc) when I get a little more comfortable with MODx.
Btw, good job on the admin interface, if any of the designers/devs is reading this ! Compared to Drupal or even Wordpress, it looks 1000 times better IMO.