Hi all, Thanks for your help !
It seems that you are missing your username:svn co svn+ssh://ericmaeker-guest@svn.debian.org/svn/debian-med/ trunk/
Ok this way all works great.
note also that Alioth uses SSH keys and not passwords for login: http://wiki.debian.org/Alioth/SSH
I'm working on different computers, but I'll read these documentations. Thanks. Eric