Download the appropriate ZIP install file for Eclipse 3.2 or 3.2 and follow the OSX installation instructions here.
The installation process is a bit more difficult than we would like. Unfortunately, it is required due to the way that GWT is implemented under OSX. In order for GWT Designer to work properly with MacOS X, it needs to use SWT classes provided by the GWT installation. The GWT Designer install process will generate a new Eclipse SWT Plugin from the GWT classes and copy it into the Eclipse plugins directory. In addition, the GWT custom WebKit frameworks will be copied into the Eclipse plugins directory as well as the custom SWT native libraries. Your system frameworks will not be affected.
Why is all this necessary? Read on...
The SWT Browser widget on MacOS X embeds the MacOS X native Safari browser whose core is a WebKit framework installed in the OS. When running GWT in "host mode" (without being deployed to the server) it uses the JavaScript Native Interface (JSNI) to redirect Java code invocations into JavaScript code invocations. This is the main principle behind how GWT "host mode" works. A part of the system WebKit framework (JavaScriptCore) doesn't provide the public API needed by JSNI to run GWT code in hosted mode. That is why GWT provides a custom WebKit with JavaScriptCore's API made public as well as a set of custom SWT classes which are built against this custom framework in the GWT distribution. GWT Designer utilizes the same principle to display truly native designed forms and can't run with the system WebKit framework for the same reason as the private JavaScripCore API.
