If you're installing as of 2009, the Eclipse downloaded from the Ambient site includes Ambient so you don't need to do an Ambient install afterward.
Open a browser, navigate to http://www.cs.duke.edu/csed/ambient and then to either Windows or Macintosh. The screen shots below are for the windows install.
Choose the default Open with option as shown:
After the download completes, choose Extract all files as shown:
In selecting the destination folder choose c:\eclipse as shown in the dialog below.
Then wait a while while the progress bar shows you that things are happening:
Find the Eclipse program by selecting the folder, then double-clicking the Eclipse application inside it. The folder is shown below in its default c:\eclipse location (use the Explorer window to find it)
The first time you launch eclipse it will ask you for the location of your workspace folder. Do not use the default shown below.
Instead, click the Browse button, navigate to the My Documents folder, click on Make New Folder and make a folder in My Documents called workspace as shown below:
Select the workspace folder, click the OK button, then wait for Eclipse to start.
Choose the Help menu then the Software Updates sub-menu, then Find and Install as shown here:
Choose a new update site as shown below, then click ok and install Ambient.
