Add a new value id to a new thread?

[henrikdam]

Hi guys,
I want to be able to add an extra id to a new thread, and save it along with the other thread info in the mysql database when the users submits the new thread.
It should work like this, so when they click the link to open a new thread:
http://www.mysite.com/newthread.php?...1&extraid=5000
it would add the value "5000" in a field in the database when they submit the thread.

My trouble is I don't know where in the codes the values are inserted in the database. I can see that vBulletin is not working like "normal" php which I am used to work with. Then it would just be something like "INSERT INTO".

I hope you can help me. It should be pretty simple if you just know where to put the right values.

Kind regards
Henrik