I installed Eclipse Indigo. At that time, I did not install the JavaEE edition of Indigo. Now I want to have the capabilities of JavaEE in my Indigo. Which plugin I should use for this. So that I can add Tomcat server and can get HTML/JSP syntax highlighting.
Following is my eclipse version screenshot.

Eclipse Web Tools (WTP). Here’s the update site: http://download.eclipse.org/releases/indigo/.
Note however that Eclipse Java EE edition contains some other features and plugins apart from WTP, so I would strongly encourage you to install fresh version of Eclipse Java EE and just connect it with your existing workspace.