Ok, so, I've been banging my head against the wall for an hour or so, and I feel an idiot..:

I've just moved a vbulletin 4 forum to nginx, and for some arcane reason,
these URLs work: http://mysite.com/forumdisplay.php?f=25
but these do not
http://mysite.com/forumdisplay.php?25-Forum-Name
(the second URL is a built-in "friendly url" function in vb4)

So, since I couldn't find anything in the logs, I decided I'm going to simply rewrite those non-functioning URLs to the functioning ones..

In short, I want to rewrite this:

http://mysite.com/forumdisplay.php?25-Forum-Name

to this:

http://mysite.com/forumdisplay.php?f=25

My attempt is this:
rewrite ^/forumdisplay\.php\?([0-9]+) /forumdisplay.php?f=$1;

Apparently, no matter how I escape it, inserting the "?" after forumdisplay.php causes the regex to not match at all.

Could any of you show me why it isn't working, please?

Thanks