Do you know any GUI builder for SWT, which is compatible with Eclipse Juno (4.2)?
The correct entry site for the window builder would be http://www.eclipse.org/windowbuilder/. The Google update sites still work, but the Window Builder is now an Eclipse project, and the main update sites are hosted at Eclipse. There you'll find also the link to the official update site for Juno (http://download.eclipse.org/windowbuilder/WB/release/R201206261200/4.2/) and a link for a ZIP download of the update site.