mySQL/PHP Coding - Help selecting/applying values

[starsitesnet]

Trying to write a hack that will allow custom overall headers based on forum (based on a similar hack found here). I've managed to get the forumdisplay part working correctly, but am having some trouble getting the custom header to show up in showthread.

I know I need to select the forumid from the thread table, and then apply that value towards the custom header (header being based on the forum you're in).

This is what I have to select forumid from the thread table:

PHP Code:

$firstid = $DB_site->query_first("SELECT forumid FROM thread"); 


The part I can't figure out is how to take the value returned from that query and apply it towards the query for the custom header.

This is what I have for selecting whether or not to use the header and the value for the custom header, based on forum:

PHP Code:

$mytop=$DB_site->query_first("SELECT enableheader,userheader FROM forum WHERE forumid=$firstid['forumid']"); 


Looking for any help here; I don't claim to be an expert .