Steps to install Force.com IDE in Eclipse:
1. Start Eclipse
2. Go to Help–> Install New Software…
3. Click Add button.
4. In Name type as Force.com IDE and in Location type as http://www.adnsandbox.com/tools/ide/install/
5. Click Ok.
6. Check the checkbox near Force.Com IDE.
7. Click Next and complete the setup.
Or visit the below link
Cheers!!!