Thanks everyone for your quick reply's! i don't even know if the sites you suggested is the one i am looking for but they are very nice!
I do remember that the background of the forum is mainly white (or some light color), and the title of the forum is unusually big and spread across the width of the page, but the design could have changed over time. Also I think it's not part of a larger general modeling forum, but is dedicated to automobiles.
Anyway thanks again! You really can count on the nice and helpful guys on AF!