There is a new AdventureWorks family of sample databases available for SQL Server 2008 February CTP at https://www.codeplex.com/Release/ProjectReleases.aspx?ProjectName=MSFTDBProdSamples. The AdventureWorks 2008 family of databases demonstrates some of the new features of SQL Server 2008. This family of databases can only be used with SQL Server 2008 and will not install successfully for earlier versions of SQL Server. The original AdventureWorks family continues to ship for SQL Server 2008, so you have a choice of staying with the compatible schema or trying out the new SQL Server 2008 features depending on which installers you download. The installers for the AdventureWorks 2008 family all have 2008 in their names. See the link above for additional details.
Right now most samples are compatible with the AdventureWorks family not the AdventureWorks 2008 family. As samples are migrated to the new schema the readmes for the samples will be updated and sample and snippets scripts will have statements like USE AdventureWorks2008 in them instead of USE AdventureWorks.