Can someone tell me if vBulletin has a way to grab a specific users profile field, say field18, in php? Or if vBulletin does not have a built in function, where in the database is the value saved for the specific user?
You can call fetch_userinfo() in includes/functions.php. You're not talking about the "current" user, right, because then it would already be in $vbulletin->userinfo['field18']. Also, if you need it in the postbit for that user's post, it will be in $post['field18'].