Eclipse 3.3:
Click [File]/[New]/[Project...] in Eclipse main menu
Select Web/Dynamic Web Project click Next.

Type Project Name, click Next.
Select ZK Supports in Project Facet list, click Next.

If you don't want to modify the default directory of Context Root, Content Directory, Java Source Directory, just click Next.
On the next page you can choose which ZK packages you want to use for this Dynamic Web Project. It will automatically choose the default ZK packages configured in the ZK Packages preferences page in Preferences Window of Eclipse.

You can select other ZK packages installed in Eclipse by click the combo box.
Click Finish, the New Project Wizard will setup a Dynamic Web Project ready for development.
Eclipse 3.4:
Click [File]/[New]/[Dynamic Web Project] in Eclipse main menu
Type the project name, click "Modify..." in the Configuration Column

On the left side of pop-up Project Facets Window, select ZK Supports, then Click OK.

Click Next
If you don't want to modify the default directory of Context Root, Content Directory, Java Source Directory, just click Next.
On the next page you can choose which ZK packages you want to use for this Dynamic Web Project. It will automatically choose the default ZK packages configured in the ZK Packages preferences page in Preferences Window of Eclipse.

You can select other ZK packages installed in Eclipse by click the combo box.
Click Finish, the New Project Wizard will setup a Dynamic Web Project ready for development.
Tips:You can see a ZK mark on the project's right top icon to indicate that this project is support ZK:

You can create new ZUL file via [File]/[New]/[File] command in Eclipse main menu.

But you have to input the ".zul" extension for that file yourself, and the newly create zul file will be empty content without any template code inside.

There are two ways to open New ZUL File Wizard:
Right click on the opened project which has been created as Dynamic Web Project in "Project Explorer" view or "Package Explorer" view, select [New]/[ZUL].

Click [File]/[New]/[ZUL] in Eclipse main menu when you select an opened project which has been created as Dynamic Web Project.

Type the file name and optional page title name, click Finish.

The newly created ZUL File will be opened in ZUL Editor.
To run the ZUL File (that is, to run a ZK Web application in Eclipse), follow the instructions:
Configure Apache Tomcat server configuration in Eclipse:
You have to create a valid Apache Tomcat server configuration of the Apache Tomcat Server (The extracted tomcat zip file which is described in Application Severs section) in Server/Runtime Environments preference page in Eclipse's Preference Window.

Please refer to the "Choose a Server Runtime Environment" section in the "WTP Tutorials – Building and Running a Web Application" article on Eclipse website: http://www.eclipse.org/webtools/community/tutorials/BuildJ2EEWebApp/BuildJ2EEWebApp.htmlOr you can refer "2.Define a Server Runtime" in this smalltalk:http://www.zkoss.org/smalltalks/eclipse/ek.html
Create a Server instance in Eclipse's Servers View:
Please follow the "Create a Server" section in the "WTP Tutorials – Building and Running a Web Application" article on Eclipse: website http://www.eclipse.org/webtools/community/tutorials/BuildJ2EEWebApp/BuildJ2EEWebApp.html or refer "3.Define a Server Instance" in http://www.zkoss.org/smalltalks/eclipse/ek.html to create a runnable server in Eclipse.
Start server, view result:
Please refer to the "Start the Server", "Running the Application" and "Running the Application" sections section in the "WTP Tutorials – Building and Running a Web Application" article on Eclipse: websitehttp://www.eclipse.org/webtools/community/tutorials/BuildJ2EEWebApp/BuildJ2EEWebApp.html
Tips:
There's a detailed step-by-step tutorial to start using Tomcat with Eclipse on coreservlets.com: http://www.coreservlets.com/Apache-Tomcat-Tutorial/eclipse.html