Question as stated in the title: how to install the GlassFish Server Adapter on Eclipse Helios 3.6?
Eclipse Helios already have the correct source to download the glassfish plugin but, the site is not available yet. The site will be available at the end of july according to this https://bugs.eclipse.org/bugs/show_bug.cgi?id=312912
You can use a development update site to install a rc version of the glassfish plugin for helios witch is:
http://download.java.net/glassfish/eclipse/helios
Add this to your update sites and then uncheck the option "Group items by category" and you will see and be able to install the Glassfish Plugin in Helios