Thanks for sharing the bb code Gary, but I would prefer to kame this hack works (but I will make the ed2k tag available as an alternative, for sure !)
I just quit testing different things, and it appears that only the opening bracket poses problems.
I tried to modify some things in the regexp, but it's just too complicated for me
edit : The @ character is also a problem, as it sees a part of the link as an email adress