2.1) Details on how to install the Android development on top of Eclipse can be found at
http://developer.android.com/sdk/installing.html YOU MUST READ THIS FIRST TO UNDERSTAND ALL THE STEPS.
2.2) You must download java sdk first from java.sun.com (get latest version)...Eclispe requires JDK to run (it is itself a Java program). This is #1 ABOVE. This SHOULD already be done if you did step 1 first as you should have.
2.3) IMPORTANT: install the RCP version of Eclipse as directed in "step 1" of the android instructions in 2.1 and you will get support in Eclipse for multiple languages (including PHP, Java, etc). It is CRITICAL that you install the RCP version.
2.4)OPTIONAL (may not be required) alter eclipse.ini file located in installed directory to point to java virtual machine installed in step #1 Read details here http://wiki.eclipse.org/Eclipse.ini
specifically you add the entry
-vm
C:\path to your jdk\bin\javaw.exe
the acutal path will be whatever it is on your machine...find the javaw.exe file from step 1
2.5) at this point you have completed "Step 1" in the Android instructions pointed to in 2.1 ...now you need to continue and finish installing and setting up (please do this) the Android SDK for use in Eclipse. Please confirm it is installed by bringing up and running the test program referred to in the Android instructions as the "Set up the Hello World application" which is found at http://developer.android.com/resources/tutorials/hello-world.html