Now for my question: I converted my old forum (based on the "mingle forum" plugin for wordpress) to Xenforo with a small script created for the purpose, everything it's ok so far.
I just can't find a way to embed in an easy way a flickr image. I run a photography forum, and everyone by now is used to just put the link of the page that contains the image ( like http://www.flickr.com/photos/playerdue/5701115239/in/photostream ), and than automatically the url turns in the proper image, linked with the page. I read that the developers of XenForo don't want to add an automatic feature, and it's ok for me, I have no problem using the media tag, but I don't know exactly how to configure it for flickr, considering that the urls used by flickr contain other variable like the name of the user, the id of the photostream, and so on.
Thanks for the help!