The most recent SDK update (Version 1.1.9 - Feb 2, 2009) includes a nice little feature, a remote API. Look at the module
google.appengine.ext.remote_api and you'll find this description in the stub:
This allows easy remote access to the App Engine datastore, and potentially any of the other App Engine APIs, using the same interface you use when accessing the service locally.
See the documentation in remote_api_stub.py.