Flash is for designers, Flex is for programmers

I needed to learn flex for a project, what is Flex? http://en.wikipedia.org/wiki/Adobe_Flex
in short, flex is AJAX nerdy cousin, and both are used to develop Rich Internet Applications (RIA). The advantage of Flash is that it will look the same on all browser (pixel to pixel likeness), and it is a true write-once-run-everywhere. it can run from a browser, using Flash player, or it can run on desktops, using Adobe AIR.
Adobe has released the Flex SDK for free, but their IDE for making Flex application (Eclipse-based) cost around $1000 to get a licence.

What’s the difference between Flash and Flex? the answer is in the title, and here http://kanuwadhwa.wordpress.com/2007/08/03/choose-the-best-flashflex/

So, how can I learn Flex for free and develop free RIA applications? ( I spent 3 hours on this and it is what this post is all about)
My friend Sirisian has the answer here http://www.kirupa.com/forum/showpost.php?p=2229691&postcount=9
The post is actually an answer to someone wanting to develop flash games, so it can be used for games as well.

I hope someone saves 3 hours thanks to this,
Have a nice day