Google App Engine - How to get demos to work?

I'm embarrassed to have to ask this, but I can't for the life of me figure out what I'm doing wrong.

I've downloaded the appengine-java-sdk-1.4.2 via the eclipse 3.6 plugin as per the instructions on Installing the Java SDK page. I am running开发者_C百科 Mac OSX 10.5.8 with JRE version 1.5.0_26. I have made the dev_appserver.sh file executable (chmod u+x dev_appserver.sh) and when I attempt to start the app server with one of the demos via the command

 bin/dev_appserver.sh demos/guestbook/war/

I get the following output, but the server does not start up:

2011-03-13 17:52:43.404 java[839:80f] [Java CocoaComponent compatibility mode]: Enabled
2011-03-13 17:52:43.405 java[839:80f] [Java CocoaComponent compatibility mode]: Setting timeout for SWT to 0.100000
********************************************************
Warning: Future versions of the Dev App Server will require Java 1.6 or later. Please upgrade your JRE.
********************************************************
Mar 13, 2011 9:52:44 PM com.google.apphosting.utils.jetty.JettyLogger info
INFO: Logging to JettyLogger(null) via com.google.apphosting.utils.jetty.JettyLogger
Mar 13, 2011 9:52:44 PM com.google.apphosting.utils.config.AppEngineWebXmlReader readAppEngineWebXml
INFO: Successfully processed /Applications/eclipse_3.6/plugins/com.google.appengine.eclipse.sdkbundle.1.4.2_1.4.2.v201102111811/appengine-java-sdk-1.4.2/demos/guestbook/war/WEB-INF/appengine-web.xml
Mar 13, 2011 9:52:44 PM com.google.apphosting.utils.config.AbstractConfigXmlReader readConfigXml
INFO: Successfully processed /Applications/eclipse_3.6/plugins/com.google.appengine.eclipse.sdkbundle.1.4.2_1.4.2.v201102111811/appengine-java-sdk-1.4.2/demos/guestbook/war/WEB-INF/web.xml

I see the warning about upgrading the JRE, but I don't think this is the problem, as there are no exceptions reported. It just won't start up. I've tried creating a hello world app from within Eclipse using the plugin and running as Web server, but that also spits out the same text but does not start up the web server.

Any idea what I'm doing wrong and how to remedy the problem?

By changing the line in dev_appserver.sh to

/System/Library/Frameworks/JavaVM.framework/Versions/1.6.0/Commands/java -ea -cp "$JAR_FILE" \
  com.google.appengine.tools.KickStart \
  com.google.appengine.tools.development.DevAppServerMain $*

instead of using the default java (which is set to 1.5.0_26 as I mentioned earlier) the web server starts up.

I had the same problem and simply tried running Eclipse as Administrator and then debugging worked fine.