The src folder in the beta download is missing the gwt.xml file, properties files and resources. Is this intentional? I ended up copying these out of the jar file to get the samples running in hosted mode.
The src folder only contains the java source files and is only there as a reference. You should not add the folder to your project's classpath, rather, just add the gxt.jar. All you need to do is inherit the gxt module and those files will be included. Let me know if you still have problems.