A good tutorial about a flash app that exports a selected movieclip to a bitmap image?

I don’t know of any tutorials but it is actually pretty simple. Any display objects that subclass DisplayObject also implement the IBitmapDrawable interface and thus can be passed to a BitmapData‘s draw() method. From there you can use one of the PNG or JPEG encoder libraries out there (Adobe’s own utils library on Google Code is best) to compress the file. Then you can send it as a binary stream over a socket connection or Base64 encode it and post it to your web server via the methods and classes in the flash.net.* package. I’ve made a few apps like this already for various clients. Feel free to message me if you’ve got specific questions.