I've tried to install this http://www.thinktecture.com/resourcearchive/tools-and-software/wscf
it seems I have to download the vs2005 version first and then update with a file for vs2008.
But the addin failed to install as for me.
Did someone achieve to do so with VS 2008 ?
You're right. It looks like it is needed to have VS 2K5 before being able to use this add-in. I guess the setup for VS 2005 tries to add a toolbar or some menu items, so it launches VS 2005, which of course fails if you don't have it.
Instead of preparing a setup program for VS 2008, the author just provides an updated .addin while for it. Maybe it is enough to extract the files from the .msi (see the back room tech for a link) and then install the .addin file from the zip of the "2008 version".
If you succeed in doing this with the msi, put then this .addin file in a directory where VS 2008 looks for it (see the list in Tools / options / Environment / Addins Macro security). Inside the .addin, there is the path to the add-in itself, which must be of course adapted.