First, be sure to read Building ODE to learn how to install Ruby, Rake and Buildr.
At the root of the checkout, run
rake package
Still in the root,
rake eclipse
In Eclipse,
File -> Import -> Existing Projects into Workspace
then select the root directory of your Ode checkout (e.g. ode/trunk)
It's generally recommended to have a dedicated Eclipse workspace for Ode, since there's a fair amount of code and projects.
