Yop, merci mais ça ne passe pas.

Options +FollowSymLinks +ExecCGI

<IfModule mod_rewrite.c>
RewriteEngine On

# uncomment the following line, if you are having trouble
# getting no_script_name to work
#RewriteBase /

# Pour ancien système
RewriteRule ^/?rub=topic&topic=([0-9]*) http://www.monsite.fr/sujet/$1/ [R=302]

.....etc.....