Ok the solution was quite easy :
The integrated 'browse' function is not the same in Windows 7 (no big surprise here) so, the only thing that fails being that (and the redirect to windows vista default logon .. duh) the simple thing to do is to just find another way of getting a new logon screen in there.
And, for that you just need to download a .logonvista file and doubleclick it, the rest works like a charm (ofc, the visuals are exactly vista ones for logon screen ...).
No need for complicated registry hacks, just have a winvista vmachine somewhere for editing, or use one of the already available and very nice thingies they have on their resource website (something like wincustomize or stuff... . com ofc-).
And uh .. this was a...