Filtering out forums based on a variable

[p0lar_bear]

I'm attempting to create a modification that will grab a specified variable from a url (i.e. index.php?filter=forumset1) and filter out forums that don't have that identifier applied to them.

I've already modified my forums table and the backend forum editor to include this new column. What I'm aiming to do is basically get vBulletin to grab the "filter" variable from the URL, and either make it so the board only drops the forums with the correct filter ID into $vbulletin->forumcache, or simply ignore boards without the correct filter ID already in $vbulletin->forumcache when generating the HTML. I'd prefer the former, though, if it's at all possible.

I'm no whiz at PHP, but I'm not a newbie to it. I've messed with phpBB and IP.Board in the past, but vBulletin is new ground for me, and the way things work code-wise is extremely confusing and hard to follow. I've tried backtracking from index.php and reading the API, but all that's led me to is a depreciated function that starts with a die() and is commented out in every file it appears in.

--------------- Added [DATE]1203483030[/DATE] at [TIME]1203483030[/TIME] ---------------

Bump.

Forgot to include what I'm looking for in obvious words. %)

I'm looking for basically where $vbulletin->forumcache is initially populated, or for how exactly forum bits are generated.

Also, is $vbulletin->forumcache a PHP array version of the forums table? Would custom columns in that table appear in $vbulletin->forumcache without any extra coding?