Are you trying to turn them away from programming? That book is a little heavy for a designer to learn.

If you're already a web-designer I'd suggest learning HTML and CSS which are used to turn your designs into marked up and styled pages. Then a easy transition is learning JavaScript which is a programming language and will nail down the basics of programming and how they apply to what you are already familiar with.

Then you move on to Knuth books when you want to branch out from JavaScript.