> and put as filter:
> +/forum/forum.php?thread_id=*[0-9]&forum_id=128082
> But it didn't work. It tried to download the whole site.

Well you first need to define a restriction. The best one is:
-*
which will exclude everything but the URL you point to.

So start with that, then build up your inclusions:
+*/forum/forum.php.....
+*.jpg +*.gif