Hi Steve
Reading your error twice I spotted that it does not complain about the (google) gwt plugin but it misses:
* org.eclipse.jst.enterprise_ui.feature.feature.group 3.2.0
I guess that you're not using a JEE edition. You'll then have to add the WTP update site manually by adding the following software site:
* http://download.eclipse.org/releases/helios
You dont need to install WTP manually, The software installer should now find your missing dependcy when you install our integration plugin.
You may of course also install WTP manually:
Go to the "Web, XML, and Java EE Development" cathegory and check "Eclipse Java EE Developer Tools"
Cheers
André