Ah thanks guys.
I was following
Sony PRS-T3 Custom Fonts Tutorial and Korben Dallas has a mistake in his URL. The way that he laid out the folders, he needs a .../Sony_Reader/... inserted in the middle.
I moved things around and it works for me.
Now that I am trying different fonts, it reminds me of the limitations on Sony's T3. Because the user isn't allowed to adjust line height, and because different fonts have different x-height proportions, I have to keep futzing with the line height in CSS every time I try a new font. Argh.