Transparant Windows

Hi everyone;

I've just started with my first WindowBlinds skin... and I've got a little problem.

I would like to make the window borders transparent with shadow around it.

this is the result I would like to have;


And this is what I get in SkinStudio and when I apply it;

(just pay attention to the window borders...)
Bad preview I know ...

So can anybody help me with this? If there is a tutorial or something, just put the link and I'll do the rest

Thanks in advance, G.