Starting with Exchange 2007, the good thing about the setup wizard is that it guides you about all the pre-requisites and provides the links from where you can download them from. However, if you are installing Exchange 2010 on Windows Server 2008 (or R2) box, and if you follow the link provided by the wizard ...
You can get an evaluation copy here. Scott Schnoll had a great post on how to install the beta, with all the gotchas and a long list of pre-reqs. http://blogs.technet.com/scottschnoll/archive/2009/04/15/how-to-install-exchange-server-2010.aspx As Exchange 2010 will only run on Windows Server 2008 (64bit only), there were some known issues with the beta version with ...
