I got the following error:

java.lang.NoClassDefFoundError:
net/sf/hibernate/cfg/Configuration

while trying to do the following:

SessionFactory sf = new Configuration().configure().buildSessionFactory();

I am wondering what I missed?

thanks,

That error usually means that you are missing some of the required classes from your classpath.

You will want to make sure that you have all the proper jar files in your classpath -- I cannot rememer the main hibernate jar name right now, but it may be something like hibernate.jar.
If that does not work, you may want to add some logging or a stack trace in there somewhere to help give you clues.

Hope this helps,