Team Foundation Server 2008 can be deployed in different configurations. In 2008 release we have made the product very flexible from deployment perspective. That means now you will have many components to think about in fail over or redundancy. In this post I will focus on TFS only components for SQL Reporting services and WSS you can follow on line MSDN docs for TFS or SQL RS/WSS.
TFS can be deployed in Single server configuration or dual server configuration. We do not provide any fail over options in single server configuration (MSDN Doc: http://msdn2.microsoft.com/en-us/library/ms316473(vs.90).aspx)
In dual server scenario you have 2 machines Application Tier and Data Tier:
Data Tier: All TFS data is stored in SQL Server. Therefore you can use any of the standard SQL fail over or high availability options. You can use Clustering, SQL Mirroring or Log shipping. The failover in case of Mirroring and Log Shipping cannot be automatic. We need to perform couple of steps before mirrored databases are activated. I will have posts on Mirroring and Log shipping coming soon.
Application Tier: TFS provides warm standby Application Tier support. If you run a TFS Orcas install and if databases are already present and mapped to different application tier we automatically setup a Warm Standby server for you. Warm standby will be non functional server deployment of TFS. If your primary application tier server fails you can use TFSAdminUtil ActivateAt to activate your Standby Server.
Hope this information was helpful.