If you open and build one of the samples in the Visual Studio 2008 SDK, and see the following error, DON'T PANIC (and don't forget your towel).
Failed to retrieve paths under VSTemplate for the specified registry hive.
This is a build error you will see if the Experimental hive has not been set up for your user account on the machine. To resolve the problem, simply do the following:
In Visual Studio 2005 and earlier, the Experimental hive was set up when you installed the SDK.
Starting with the Visual Studio 2008 SDK, package development is per-user by default. The SDK installer will set up the Experimental hive only for the user who actually installed it. If you installed under a different user account than the one you use for development, you will have to "Reset" the hive with your account before you can begin package development.