如何在Eclipse Helios中的另一个项目中引用库?

We have a problem at the place that I work with referencing multiple projects in our code. Basically, we have a product, which I'll call Leviathan. This project has quite a number of other versions, each of which we maintain as separate projects in Eclipse. As developers, we typically have multiple projects (multiple versions) open in Eclipse simultaneously, as we get helpline calls about older versions (as well as developing simultaneously multiple versions).We have a problem at the place that I work with