We had a .com domain which was being associated with Google Apps email. We have recently bought a .org domain and want all users to use .org domain Google Apps email instead. As the admin, I am trying to move all user emails from the .com domain to .org domain. Is that possible, without asking the users?
Google Apps now supports multiple domains so you could probably configure both domains to work together. See http://www.readwriteweb.com/enterprise/2010/06/google-apps-now-supports-multi.php
As I understand you want to keep the part before the @ the same.
In that case, just add the new domain as domain-alias. You can find more info on http://www.google.com/support/a/bin/answer.py?hl=en&answer=53295
Google Apps email migration enables domain administrators to transfer the existing contents of users' mailboxes from an IMAP server to Google Apps.
You simply need to enable IMAP, and the rest sounds like it should be easy.
If you just want to add the new domain to your account and have all the users appear in it then you can add a domain alias. See http://www.google.com/support/a/bin/answer.py?hl=en&answer=53295 for details.
If you're looking to eventually deprecate your existing domain in favor of the new then things get a little trickier. Currently its not possible to change your primary domain. You'll have to create a brand new account and add the domain to that, then migrate the data. See http://www.google.com/support/a/bin/answer.py?answer=54819 for more details.
Google provide some basic migration options for email, but pretty much nothing for the other "basic" Apps services. Pretty much all of the data is available via the various APIs Google make available (though most APIs are only available to Premier and Education edition customers), but you're probably stuck writing a good chunk of code to get all this running. Its not a trivial undertaking, so stick with the domain alias option if you possibly can.