New failover cluster APIs have been implemented in Windows Server 2008, and these APIs may pose interoperability issues with earlier versions of Windows

Some potential gotchas with clustering with Windows 2008. Don't let this KB article scare you away from using the updated clustering features. They are actually really nice, but it is good to get this information out there.

In Windows Server 2008, a new set of platform APIs has been implemented to provide better functionality, better scalability, and easier manageability for clustering environments. The manageability aspect includes remote management. However, this new set of failover cluster APIs also poses interoperability issues with earlier versions of Windows.

The two items that I find the most interesting from the KB article are:

1. The backup APIs have been removed in Windows Server 2008. You must now use the Volume Shadow Copy Service (VSS) writer to reach this backup functionality in a clustering environment. Additionally, several new APIs have been added, although the pre-Windows Server 2008 APIs should still function.

and

2. Because of a core protocol change in Windows Server 2008, you cannot call failover cluster APIs from earlier Windows clients to Windows Server 2008 clusters. Therefore, the new failover cluster APIs cannot be called from Windows XP or from Windows Server 2003. Currently, the cluster APIs can be called against a Windows Server 2008 cluster only from Windows Vista Service Pack 1 (SP1) or from Windows Server 2008.