Hi Rogerio,
As Ulf said, as far as building the GAE webapp, you could use Hudson to build your GAE webapp just as you would for any other webapp. As far as deploying your webapp to GAE, you could simply add a build step that executed a script similar to the following:
appengine-java-sdk\bin\appcfg.cmd --email
user@gmail.com --passin password update myapp/war
So
you should be able to build and deploy your GAE webapp without too much difficulty.
Lloyd