Vista style trans with ShellWM style skinning.
And it actually works too. The interesting bit here is that at first glance it looks like a tool to make your XP look like Vista somewhat (why anyone would want to do that is beyond me), but if you poke around a bit, you'll find that you can change the graphics and create your own skins with alpha transparency. Too bad it's just the borders.
Ya, it's just to add alpha trans to VSs, really. You can use it as a windows skinner, but why with VSs? I have to wonder if it would work on 2000. Then we would have something. I don't think it's supported though.
Perhaps it works if you have GDI+ installed. A lot of XP stuff that adds translucency requires that.