Star Stacking is a relatively new technique in Astrophotography. It allows the photographer to utilize the capability of his/her camera's ISO to get the best dynamic range in a shot, and THEN stack the images to make the stars POP and reduce the noise. The BEST software for automatically stacking stars is called Starry Landscape Stacker. It's only available for Mac computers (another good reason to switch to a Mac) and it's only $39.95 in the Apple store.
As a substitute for the (inadequate) Windows PC there is a manual process which can be done in Photoshop. I've embedded the video below. Many thanks to Ian at LonelySpec. Note**I've tried this manual method several times and never gotten it to work right, so I really recommend trying either Starry Starry Landscape Stacker, or the ones listed below for Windows.
Now, on to my demo of the Starry Landscape Stacker.