I'm using Cactus from the Jakarta project with great success. (http://jakarta.apache.org/cactus ). Essentially, it's a web app that you incorporate into and deploy along with your j2ee app. Then you have your test cases extend one of their junit.TestCase subclasses instead of the JUnit TestCase.
You then call your TestCases in standard JUnit fashion, and the Cactus framework takes care of redirecting your calls to their web app (which IS running in your local interfaces' JVM) and marshalling the results back to you. It's slick, it's easy, it's hip, it's happening!