If you want to try out Data Services with the SharePoint 2010 Beta today you have to use CTP2 of Data Services v1.5, because unfortunately the Data Service RTM version, aka the Data Services Update for .NET 3.5 SP1 is incompatible with the SharePoint 2010 Beta.

This is a point in time issue – when SharePoint RTMs it will work seamlessly with the Data Services Update for .NET 3.5 SP1.

Alex James
Program Manager
Microsoft