Microsoft issued a press release announcing the both the public beta of SharePoint 2010 and its general release. The public beta will be available November 2009, along with the public betas of Office 2010, Project 2010 and Visio 2010. The general release for SharePoint 2010 is slated for the first half of 2010.
From the Microsoft press release:
The public betas of Microsoft SharePoint Server 2010, Office 2010, Project 2010 and Visio 2010 will become available in November 2009; more information is available at http://go.microsoft.com/?linkid=9689707.
Microsoft SharePoint Server 2010 will be available in the first half of 2010. More information about Microsoft SharePoint Server 2010 can be found at http://www.microsoft.com/sharepoint.
Remember that SharePoint 2010 will be an x64-only release. That means you will need to install it onto an x64 version of Windows Server.