Also, for what it's worth, people can get active topics for arbitrary forums by using the following url scheme utilizing one of the newer features I added to the forum:
http://www.hydrogenaudio.org/forums/index.php?act=search&CODE=getnew&active=1lastdate=(cutoff)&activeforums=(forums)
Where "cutoff" is everything newer than x seconds old and "forums" is a set of forums denoted by a list of comma separated forum id's.
So to get the active topics for the music and off-topic section, you might use
http://www.hydrogenaudio.org/forums/index.php?act=search&CODE=getnew&active=1lastdate=259200&activeforums=17,39
To get the compliment of the set of forums, or to get active topics for all forums except those which are listed, add &compliment=1 before lastdate, like so:
http://www.hydrogenaudio.org/forums/index.php?act=search&CODE=getnew&active=1&compliment=1&lastdate=259200&activeforums=17,39
This will get all forums not in the set of forums listed, or in other words will return active topics for everything except the off-topic and music forum.