Installing ADT in Eclipse

1. Start Eclipse, then select Help > software Updates.... In the dialog box that appears, click the Available software tab.
2. Click Add Site
3. Enter the following url:http://dl-ssl.google.com/android/eclipse in the Location field of the Add Site dialog box. Click OK.
4. Back to the Available software interface, click Expand Http://dl-ssl.google.com/android/eclipse to see a list of plugins included in the URL, including Developer Tools. Select the check box next to Developer Tools and click Install.
5. In the installation window that appears, the selected Android DDMS and Android development Tools should appear. Click Next.
6. Read and accept the license agreement, and then click Finish.
7. Restart Eclipse.

Eclipse 3.5 (Galileo)

1. Start Eclipse, then select Help > Install New software.
2. In the Available Software dialog box, click Add....
3. In the ADD Site dialog box, in the Name field, enter the name of the remote site (for example, "Android Plugin"). In the Location field, enter the following url:https://dl-ssl.google.com/android/eclipse/note: If you encounter problems accessing the plugin, you can change the HTTPS in the URL to HTTP (using HTTPS is a bit more secure). Click OK.
4. Back to the Available software interface, you should see the Developer Tools option in the list. Select the check box next to Developer tools to select both Android DDMS and Android development tools. Click Next.
5. In the final Install Details dialog box, features such as Android DDMS and Android development Tools are listed. Click Next to read and accept the license agreement, install all dependent components at the same time, and then click Finish.
6. Restart Eclipse.

http://blog.csdn.net/greenappple/article/details/6170478

Installing ADT in Eclipse