Regex for matching anything after particular directory

Regex for matching anything after particular directory

I have a page set up on my wordpress install called /forum.
I want anything that comes after forum e.g. /forum/login.asp?helloworld=hi
etc to be put as a query string to forum so it goes to the forum page and
I can obtain this 'login.asp?helloworld=hi' as a variable.
I've created a rule on my IIS server which is above the default wordpress
rule.
I used this regex:
/forum/(.*)$
to rewrite to this /forum/?test={R:1}
and made it so it stops processing any other rules if we get a match.
All I seem to get is the Wordpress 404 page. Im absolutely useless at
redirects/rewrites/regex etc so any help would be awesome!