Here's a guide for installing SDK in Ubuntu easily:
http://wiki.maemo.org/Documentation/..._GUI_Installer

After you have MADDE & SDK installed and you have done everything you want inside MADDE, you can then copy your theme-project folder into SDK and then pack it up there with typing following command inside scratchbox / your theme directory: "dpkg-buildpackage -rfakeroot". First time it will tell that you're missing some depencies so you need to manually install them with apt-get install -command.

It's kind of not-so-easy to set-up, but after you've got yourself a working development platform it's easy to produce themes.

And also if you want to upload your stuff into extras-devel or extras, you should read this:
http://wiki.maemo.org/Uploading_to_Extras-devel

But that's enough of off-topic You might want to create a new topic under Developement -category?