I often get asked similar questions about my class. Following are some questions & answers.
You could look over past syllabi & look at some of the suggested readings. Don't freak if you don't "get it" right away—this can be a bit overwhelming at first, but I gently walk folks through everything.
Many, many students have found this site to be very helpful:
I don't agree with everything that W3Schools teaches you, but we'll sort that out in class. :)
No, you don't need to purchase any books. I don't require any books in class at all—everything you need is on the Web.
If you do want to check out a book, I highly recommend Jeffrey Zeldman's Designing with Web Standards. It's a darn good book, but it's not a guide to coding. Instead, it's an overview as to why we'll do things in a certain way.
Unless you do absolutely nothing, never try, & never learn anything, you'll be fine grade-wise. Try your best, and you'll get a good grade. My goal is make sure that people learn, not to hold grades over their heads.
My syllabus is on my website. The course is in 2 semesters: in the Fall, we learn HTML and CSS (Cascading Style Sheets), and in the Spring, we cover CSS the entire time. You can only take the first semester if you'd like, but most students end up taking the Spring course as well.
You can see old syllabi at the Archives.