You will need Microsoft Visio Standard or Professional in order to view and use these stencils correctly. The files listed for download on this page are .vss (Visio stencil) files within .zip files. Some of the .zip files contain Microsoft PowerPoint files in addition to Visio files. The PowerPoint files contain .emf (enhanced metafile) vector images derived from the Visio drawings. These may be copied and pasted into PowerPoint and other applications without requiring Visio.
If you are a Mac user, the stencils will also work with recent versions of OmniGraffle (by Omni Group), a Visio-like application for the Apple Mac platform.