I just installed Eclipse Helios (Java EE edition) and tried to install the Google App Engine plugin for Eclipse.
I get the following error:
Cannot complete the install because one or more required items could not be found.
Software being installed: Google Plugin for Eclipse 3.5 1.3.3.v201006111302 (com.google.gdt.eclipse.suite.e35.feature.feature.group 1.3.3.v201006111302)
Missing requirement: Google Plugin for Eclipse 3.5 1.3.3.v201006111302 (com.google.gdt.eclipse.suite.e35.feature.feature.group 1.3.3.v201006111302) requires 'org.eclipse.platform.feature.group [3.5.0,3.6.0)' but it could not be found
Is it only possible to add the plugin to Ganymede - not Helios?
There is a version of the GAE Plugin for Eclipse 3.6/Helios listed on the Download page - did you try this?