I'd like to develop, is there a hello world walkthrough?

By doing a quick search looks like I need Debian / Maemo 5 Beta 2 SDK / Scratchbox installer

Anything else? What next??

Thanks

There are instructions for installing the SDK at
http://wiki.maemo.org/Documentation/...l_Installation
You need to be running Linux. If you are on Windows, a user here called Nathan is working hard to make an easy-install package with Windows Virtual PC; a Ubuntu image and scripts to auto-install everything. Documentation with links to download and installation instructions is here:
https://garage.maemo.org/plugins/wik...id=1033&type=g
There is talk about it in this thread:
http://talk.maemo.org/showthread.php...ht=sdk+windows

Regarding hello-world tutorial etc, there is a developer guide here:
http://wiki.maemo.org/Documentation/...eveloper_Guide
There is a graphical UI tutorial there with a simple helloworld and more.

HTH

EDIT: FYI, the final SDK is released, so that is where my links point (didn't register at first that you mentioned the Beta 2 SDK in your post).