This post was from a few days ago however I just saw it today.. It looks like the Exchange Development team has completed the Exchange 2010 code and it is on its way to General Availability (GA). Read more of the details over on the Microsoft Exchange Team’s Blog:
http://msexchangeteam.com/archive/2009/10/08/452775.aspx
If you’re interested, you can still get the Release Candidate (RC) version of Exchange 2010 from Microsoft here: http://technet.microsoft.com/en-us/evalcenter/dd185495.aspx
System Requirements: http://technet.microsoft.com/en-us//library/aa996719(EXCHG.140).aspx