As of today (May 5th 2010) you can download Project Server 2010 from the Subscriber Downloads section of MSDN at https://msdn.microsoft.com/en-us/subscriptions/securedownloads/default.aspx or your locale specific subscriber downloads page. Many different languages are already available (use the drop-down to select) and still more to come. You will also need SharePoint Server 2010, with an Enterprise key, and in the same language as Project. The Project Professional and Standard client in both x86 and x64 are also available (posted a week or so ago). Look in the New Downloads section, or if you are reading this in the future (my future, not yours) then the Servers section.
As a reminder, Project Server and SharePoint Server 2010 are x64 only, and require x64 SQL Server. You might like to try the newly released, and available from the same download, SQL Server 2008 R2. At the time of writing I’m Still waiting for a support announcement on this version for production use, but certainly for testing you should have no issues.
The client come in both x86 and x64 – but you cannot mix and match different programs from the Office suite (including Visio, Project and SharePoint Designer) on the different architectures. so all must be installed x86 or all x64. If you want to keep any 2007 programs that means sticking with x86. General guidance is to stick with x86 unless you have a good reason for going x64 – such as large spreadsheets for Excel, big master projects etc. If you have add-ins in any of your Office applications you will want to check for x64 versions before making the architectural decision.
And if you do not have an MSDN subscription, then what better time to get one! http://msdn.microsoft.com/subscriptions/default.aspx
As mentioned by Christophe late last week,you can also get the software from Microsoft Volume Licensing downloads http://blogs.msdn.com/chrisfie/archive/2010/04/30/project-2010-professional-standard-and-project-server-2010-are-ready-for-download-on-msft-volume-licensing.aspx.