If you are a Google Apps admin, here’s how you can add the new Google Sites wiki service to your account.
The procedure is simple but not very obvious because unlike Gmail or Google Calendar, the Google Sites service is not integrated with Google Apps by default.
1. Open your Google Apps Dashboard and click the "Add More Services" link.
2. You should see a button to associate Google Sites with your Google Apps account. If it is unavailable, use the following link:
Your new Google Sites website can now be accessed from sites.google.com/a/yourdomain.com.