making source files

hi:
as i saw in examples, the source files for MyGui application r:
*.skin, *.png,*..layer, *.pointer .... i know how it works and how to deal with it,
but the problem is how do i make such these files???
to make my shapes and my pointer shape what is the tool?

At the moment all this files is written without any tool "by hands".
We are working on skin editor but it's on early stages at the moment.