We use version 3.3 of Eclipse, which is also known as Europa release. You can download the IDE from http://www.eclipse.org/downloads/. We recommend using the version "Eclipse IDE for Java EE Developers".
First we have to make a file association for the .zul files. For that open the Preferences dialog with Window|Preferences. After that do the following steps:
1. Type Content Types into the search dialog.
2. Select Content Types in the tree.
3. Select XML in the tree.
4. Click Add and type *.zul.
5. See the result.
The steps are illustrated in the picture below:
With these steps, we have syntax highlighting ...