is there no official documentation / guide published somewhere on how to create components for Flash CS5?
The UI Components in Flash CS5 haven't changed since Flash CS3 as far as I've noticed.
Jeff Kamerer wrote a lengthy series on the Adobe Devnet on creating AS3.0 Components in Flash.
Here are some of the topics covered (via Robert Penner )
If you're not planning to use the V2 Component architecture, you could just use Component Definition panel to link your class properties to the Component Inspector easily.
A bit more on this in the slightly related question AS3 create component using Flash CS4.
HTH