I am using Windows XP machine and installed Eclipse Helios from the eclipse website http://www.eclipse.org/downloads/ (option Eclipse classic 3.6.2) I installed Android SDK from the Android Developer website http://developer.android.com/sdk following the instructions. The next step was to install the ADT in Eclipse. The instruction seemed straight forward - Go to Help -> Install New Software -> click Add button -> Give Name as ADT plugin and Location as https://dl-ssl.google.com/android/eclipse/ (or http://dl-ssl.google.com/android/eclipse/) if that didn't work.
This proved to be a blocker though. The installation just wouldn't complete. It always stopped with the error
Cannot complete the install because one or more required items could not be found.
Software being installed: Android Development Tools 10.0.1.v201103111512-110841 (com.android.ide.eclipse.adt.feature.group 10.0.1.v201103111512-110841)
Missing requirement: Android Development Tools 10.0.1.v201103111512-110841 (com.android.ide.eclipse.adt.feature.group 10.0.1.v201103111512-110841) requires 'org.eclipse.wst.sse.core 0.0.0' but it could not be found
Most solution websites and forums on internet gave advice about installing update plugins for Helios. This may or may not work for everyone, certainly did not work for me, because apparently the eclipse version I downloaded did need any updates.
The problem is clear - that eclipse does not have all the required plugins. The best advice in this situation is to actually find out what is missing and explicitly install it rather than chase for generic updates. The above error message for example shows - requires 'org.eclipse.wst.sse.core 0.0.0' but it could not be found. This means org.eclipse.wst.sse.core is missing. A google search gave URL to directly install it. I got this one from http://www.java2s.com/Code/Jar/DEF/Downloadorgeclipsewstssecore11201v200706212223jar.htm.
This standalone installation into Eclipse plugin folder, sorted out the problem and I could complete ADT plugin installation after this.
