What I usually do is, in Eclipse preferences, I define an Installed JRE called "JDK X.Y.Z" and include tools.jar as part of it libraries. Then I change the project preferences to use that JRE "JDK X.Y.Z".
Help -> Install New Software
Choose "Helios - http://download.eclipse.org/releases/helios" site
Expand "Web, XML, and Java EE Development"
Check JST Server Adapters (version 3.2.2)