Microsoft has released the Release Candidate 0 for Windows Server 2008
Here are the links
ISO files
Windows Web Server 2008 RC0http://www.microsoft.com/downloads/details.aspx?FamilyID=d977fde8-d3fb-4e6c-8a8a-352cf83111cc&DisplayLang=en
Windows Server 2008 RC0 Standard Editionhttp://www.microsoft.com/downloads/details.aspx?FamilyID=d694d4cc-0681-41b5-b02e-012be18f8b71&DisplayLang=en
Windows Server 2008 RC0 for Itanium-based Systemshttp://www.microsoft.com/downloads/details.aspx?FamilyID=07ec6bea-b14e-4f73-98c6-eb7a92e76b05&DisplayLang=en
Windows Server 2008 RC0 Enterprisehttp://www.microsoft.com/downloads/details.aspx?familyid=0818d425-cd47-4279-be8d-24aba14530a3&displaylang=en&tm
Windows Server 2008 RC0 Datacenterhttp://www.microsoft.com/downloads/details.aspx?familyid=95cc89a8-0076-4571-b379-4aa4f526b893&displaylang=en&tm
Documentation
Windows Server 2008 Release Candidate: System Requirements and Installation Documentationhttp://www.microsoft.com/downloads/details.aspx?familyid=1087a498-40ad-46ba-9ada-f32a58a94a85&displaylang=en&tm
Windows Server 2008 Technical Overviewshttp://www.microsoft.com/downloads/details.aspx?familyid=46dc26d6-af47-43f0-b3de-521831fe09d6&displaylang=en&tmWindows Server 2008 Step-by-Step Guideshttp://www.microsoft.com/downloads/details.aspx?FamilyID=518d870c-fa3e-4f6a-97f5-acaf31de6dce&DisplayLang=en
Release Notes for this Release of Windows Server Virtualizationhttp://www.microsoft.com/downloads/details.aspx?FamilyID=3ed582f0-f844-40ba-b692-230845af1149&DisplayLang=en
Windows Media Services 2008 for Windows Server 2008 RC0http://www.microsoft.com/downloads/details.aspx?FamilyID=898fe4ff-92fc-4ab8-bd5a-6ce689004b40&DisplayLang=en