Well it's really everything I needed. But some little remarks though : the setting in the backend should be explained a little better for newbies.
breaking the wrapper is no issue anymore : in the backend, instead of using .../subfolder for the url of your forum, just insert the menu-wrapper-link, and the links won't break your wrapper anymore.

Well, I used alphacontent with my previous joomla 1.0.15 installs and when I went on using the 1.5 version, I needed a similar component. This alphapcontent 4.0.0 was just what the doctor ordered. A great component, with great support. When I had a little trouble with article-titles starting with a number, the author brought a solution within 12 hours, and that for a completely free component,...

now I'm waiting for the next version which supports special characters in titles, and then it will be truly perfect.
thanks bernard for this much needed plugin.