<p>Is there any way to show two editing windows in visual studio? I would like to look at two source files at the same time but I must be missing the option to do that.</p>

Another easy option is to open two documents, then just click and drag the tab for one of the documents and drop it on the document itself. This will display a menu that lets you move the document to a new vertical or horizontal tab group.
I find this to be the easiest and quickest way to do this.
You didn't ask in the question, but if you want to edit
one
document in two windows, you can grab the small area above the scrollbar and drag it down. You will now have your document open in two scrollable areas. Great for working on two sections at once.