Custom Window Shapes

I know this has probablly been asked before but i searched around and didnt see it (probablly because i didnt know the right terms to search for) but im sure everybody knows what im talking about. How do you go about drawing a window the shape of a car or something. Anybody got a tutorial? Thx.

The attached tutorial is from PlanetCpp.com it uses a bitmap and draws them with transparencies to create a custom window shape.

Thanks alot, that is exactly what i was looking for. On a side note, do you know if anybody has ever animated transparent windows like this one? Thats the target for the end result. That image for example, with a few minutes in paint shop could have other frames and possibly make the wings move or eyes blink.

Yeah, they have, and boy was it ever annoying I cannot imagine a more annoying and hostile user interface than a smiley face window with shifty eyes that follow the cursor.