Hello to all three of you. I'm one of the two release engineers for ReactOS
and we're happy to have anyone come and help. To at least point you guys in
the right direction, here is a link from the ReactOS site. These provide
basic tutorials on building and testing ROS (though we badly need to update
the testing sections).
http://www.reactos.org/wiki/index.php/Build_Environment
One of the difficult parts about writing the ReactOS kernel is that you need
to learn about the internals of the NT architecture. That link will point
you to at least be able to compile ReactOS, and if you have questions,
you're welcome to pop into the IRC channel like Aleksey (Fireball) said.
Possible online win32 tutorials you could take a look at are as follows:
http://www.relisoft.com/win32/index.htm
http://www.winprog.org/tutorial/
These are of course starting points that you can look at on your own. And
of course the other devs would be happy to help you (providing you can catch
them online).