How do I install a JRE or JDK to run the Android Developer Tools on Windows 7?

You can go here to download the Java JRE.

You can go here to download the Java JDK.

After that you need to set up your environmental variables in Windows:

1. Right-click My Computer
2. Click Properties
3. Go to Advanced System Settings
4. Click on the Advanced tab
5. Click on Environment Variables

EDIT: See screenshot for environmental variables