I've not looked at that specific sample, but based on the error it appears that you haven't included the reference of the pipeline project in your program's Content project.
Assuming you have both projects opened in the same solution, you can expand the Content project of the main program and then right click on References to add a project reference. If it isn't in the same solution, you will need to browse your harddrive for the assembly that was compiled from the earlier solution.
Hope this helps,
Chad
Microsoft XNA Unleashed - 2D, 3D, HLSL, Content Pipeline, XACT, Particle Systems, AI, Physics, Game States, Performance, Garbage Collection and 2 full games!