Let's get started with the installation of Android on Windows 7.
First of all, you must have a JDK (Java Development Kit) on your OS, the version 6 is the most secure one, so I recommand it.
If you do not have one, let's download it on the official website of Oracle:
Then download the Android SDK (Software Development Kit) on the official website of Android:
Once installed on your computer, launch the SDK Manager on the Android SDK directory if it does not start automatically.
On the left panel, select the Available packages and select all packages you want.
Then click Install Selected > Accept All.
It is possible that, even if you already have the JDK on your system, the executable asks you to download the JAVA SE.
Just close this window and relanch the Android executable.
If you want a fresh version of Eclipse, choose the Classic or Java one on the official website:
For its plugin for Android, you have to open Eclipse and select:
Help > Install New Software > Add
Add "ADT Plugin" for the Name and for the URL:
Check the Name Developer Tools that has appeared.
Next > Next > I accept the terms etc. > Finish > OK > Restart Now
Done! Android is installed on your Eclipse. But there is still something missing: the configuration!
Let's do it:
Open Eclipse > Window > Preferences > Android (A new window from Android may appear: click Proceed or Cancel.)
Click Browse on your right and select the Android SDK directory (where you installed it), for example:
Apply > OK
You are now ready to develop on Android and create your first application, GOOD LUCK