a) First Download and install Eclipse with Java or RCP support
Eclipse Download Page: http://www.eclipse.org/downloads/
Eclipse for RCP/Plug-in Developers (183 MB) - http://www.eclipse.org/downloads/download.php?file=/technology/epp/downloads/release/galileo/SR1/eclipse-rcp-galileo-SR1-win32.zip
b) After download just unzip it and you can start using eclipse.
c) Download and extract Android SDK - http://developer.android.com/sdk/index.html
d) Now start Installing Android Plugin to Eclipse
1. Start Eclipse, then select Help > Install New Softare.
2. In the Available Software dialog, click Add....
3. In the Add Site dialog that appears, enter a name for the remote site (for example, "Android Plugin") in the "Name" field.
In the "Location" field, enter this URL:
Note: If you have trouble aqcuiring the plugin, you can try using "http" in the URL, instead of "https" (https is preferred for security reasons).
4. Back in the Available Software view, you should now see "Developer Tools" added to the list. Select the checkbox next to Developer Tools, which will automatically select the nested tools Android DDMS and Android Development Tools. Click Next.
5. In the resulting Install Details dialog, the Android DDMS and Android Development Tools features are listed. Click Next to read and accept the license agreement and install any dependencies, then click Finish.
6. Restart Eclipse.