Is there a sample AD & LDAP server for practice?

These guys have set up a public, read-only LDAP for testing purposes:

http://www.forumsys.com/tutorials/integration-how-to/ldap/online-ldap-test-server

yes you can try it for practice

http://www.microsoft.com/en-us/server-cloud/windows-server/active-directory-trial.aspx

or you can use an open-source alternative such as:

http://directory.apache.org/