I'm having trouble with positioning Custom blocks to show up 'after' my websites forum.

The website forum is in the center column. Left to itself it looks just fine, however if I want to add extra stuff to the central column it always ends up above the forum. I would like it below the forum.

Weighting the Custom block doesn't seem to have any effect. (-1, 0, 200 and 400) all return the same result.

The forum module (CBB 3.04) doesn't seem to be treated as a standard block so I does anyone know where I can find the code that draws blocks before the CBB 3.04 module?

Thanks