Microsoft has released the first public beta version of Exchange Server 2010
You may register and download beta bits from the link below
http://technet.microsoft.com/en-us/evalcenter/dd185495.aspx
Also here are some other useful links on exchange 2010
Product Overview
http://www.microsoft.com/exchange/2010/en/us/overview.aspx
System Requirements
http://www.microsoft.com/exchange/2010/en/us/System-Requirements.aspx
Product Documentation
Videos
http://edge.technet.com/unifiedcommunications/
Nirmal Thewarathanthri