When Windows Vista was launched, I wrote a post about the volume activation (VA) 2.0 activation process. With Vista SP1, reduced functionality mode has been removed although there is still the same legal obligation to run properly-licensed copies of Windows. (Microsoft has published a Q and A sheet on the changes made to their anti-piracy programme).
A number of people have asked where they can get a 180-day evaluation copy of Windows Server 2008 and, as far as I’m aware, there isn’t one. Instead, it is possible to install the product and it will attempt online activation (there is no longer an option in setup to deselect this). If activation fails, then a 60-day grace period will commence, during which the product will have full functionality and can be activated at any time, using a key management server (KMS) if one is available, or alternatively by entering the multiple activation key (MAK) in the system properties. Re-arming is also available, allowing 3 re-arms (so up to 240 days total use before activation). That should be more than enough time for evaluation and further details are available in Microsoft knowledge base article 948472).