http://www.microsoft.com/office/preview/beta/getthebeta.mspx

SharePoint 2007 is now available for download. The quickest way to get it installed is to download WSS v3, then on an Win2003 SP1 Standard Edition server, give it the application server role, install Microsoft Windows Workflow Foundation Runtime Components Beta 2.2 (Build 3807.7), and Microsoft .NET Framework 2.0. Then set the web server to ASP.NET 2. Then install WSS v3. Not too hard, but I find a clean install of Windows is the best thing to guarantee it works. Full install instructions are included in the download. Good luck!