Thanks Xenon, though that doesn't seem to work as expected. It seemed to add one addional query for each post per page. The condition didn't seem to work also.
Basicly I need a query to check that database to see if the user who is viewing the threadid is in the database table. If he is show X if he isn't show Y. Normaly I would just add this to the showthread.php and it works fine. Though I have to add this to the postbit template. So theres no reason to run 10 extra queries when they will always equal the same thing.
The problem is getting the condition to work in the postbit template.