The RC1 bits have been made available again at the links below but please remember the following about pre-RTM code:
As this is not final release code, you may not install the software in a live operating environment.
Thus, it should not be used for customer case studies. It should be used for partners to test and check out the software (avoid migration from RC to RTM code).
Windows Essential Business Server 2008 Public Preview Software – Release Candidate 1