The nbproject/project.xml file put in place by seam-gen is broken in more than three ways. Fortunately, I have a patch for you!
So how is it broken?
1. It is configured to use "src" as the Java source folder. seam-gen, in fact, creates three source folders, src/action, src/model, and src/test (hence the broken in more than three ways comment)
2. The test package does not have any libraries, so it is impossible to start writing tests in NetBeans using TestNG and SeamTest
3. The xmlns on the java-data note should be upgraded to support NetBeans 5.5.1 (at least, that is what NetBeans 5.5.1 changed it to)
4. Take out testng.jar from the src/action and src/model compilation units