There are different ways to get Eclipse Scout. Using an update site is easier to install and allows you to stay up to date with the latest versions of Eclipse Scout.
The easiest way to download Eclipse Scout is to get the packaged distribution from the Eclipse download page.
If you have already an Eclipse IDE running, you might want to add the Scout functionalities to your current Eclipse installation. Select Help > Install new Software in the menu bar and work with the built in update site:
Indigo - http://download.eclipse.org/release/indigo

You can enter Scout in the filter text or browse through the Application Development Frameworks category.
Use the update site from Eclipse (see how):http://download.eclipse.org/scout/nightly/
Compatible Eclipse version:
You can also download the files directly and install them manually (see how)
Use the update site from Eclipse (see how):http://download.eclipse.org/releases/juno
Compatible Eclipse version:
Use the update site from Eclipse (see how):http://download.eclipse.org/scout/releases
Compatible Eclipse version:
The source code is available in the SVN repository:http://dev.eclipse.org/svnroot/technology/org.eclipse.scout
Accessing specific released versions or branches is described on our Wiki pages.