For compsci 108 please do NOT use the eclipse install on the Ambient websites. You should download the Eclipse IDE for Java EE developers from the Eclipse downloads site. You should have already installed Java 6, either from Sun Java site (download JDK 6, Update 2 as of 9/4/07) for Windows and Linux or from the Apple Developer Site if you have OS X on a mac. For the Mac you'll need Java SE 6.0 and you'll have to join the apple developer (ADC) site since this is a preview release.
After installing Eclipse you'll need to install Ambient. The information on how to do this is somewhat buried in the Ambient pages here's the information for installing Ambient from an existing Eclipse install and here's a video of me doing the complete Java/Eclipse/Ambient install on Window's Vista.