Dean,
The notebook you attached is not a Stylesheet notebook.
I have an essay A Mathematica Style that discusses how to set up a Stylesheet for your own work. It also has links to a Mathematica test notebook and a Mathematica Stylesheet that can help you get started.
Otherwise you have to start with an open notebook and use Menu/Format/Edit Stylesheet to bring up an initial Stylesheet.
The Stylesheet discussion in the essay is in terms of an application, but you could instead use the Install button on the Stylesheet to save it.
I would, however, urge you to set up your work as an application in your $UserBaseDirectory/Applications folder. Just create a folder there with a name such as 'Dean Physics Study'. Then you can add a place for Stylesheets, palettes and even add a package if you get around to it. Mathematica will automatically find everything. Maybe initially the application will just be for yourself, but later you may want to share parts of it with other people. If they unzip it into their UserBaseDirectory/Applications folder then everything will automatically be available to them. You can also include folders for your study notebooks. It's just a convenient way to organize your work, instead of having everything scattered around.
