The two variables Hanson quoted are straight from the database. Look in your user table and you will see the column "usergroupid" and "membergroupids" You will have a single number in the first one, and the second one can be empty or have several usergroup ids separated by a comma. For instance, this is for one of my admins:
Code:
$vbulletin->userinfo['usergroupid'] = 6
$vbulletin->userinfo['membergroupids'] = 13,27,31,33
The group names are defined in the table usergroup. The id is in column "usergroupid" and the name of the group is in the column "title"