There are a lot of UML and ER tools out there, but they cost a lot of money, too.
This is a step-by-step to develop your database with Eclipse and HiberObjects for free.
It is a fast way for Java developers to develop database tables.
It uses an UML-ER Model to generate JavaBeans, which can create tables on the database by using Hibernate as persistence manager.
This is a step-by-step tutorial. I made this Tutorial, because I was not happy with the four project folders generated by JBoss Tools 2.0.0 when I select a new Seam EAR project. The work is a bit confusing. If I create a new Seam WAR project I only get two projects (one of them is a test project). I had a lot of trouble with the WAR project. I was not able to not get the EJB3 examples work with it. Never the less the folder structure is different from the Seam-gen generated projects. This tutorial works completely without JBoss Tool. You can use JBoss Tools anyway, it has nice functions do build a RichFaces JSF page, but keep in mind that new generated projects are difficult to handle, since you have to keep an overview of all four projects and the changes you made in each of them.