I got it free, but I don't think I am allowed to post the link on here or anything, took me less then 5 minutes to find on google though, just download it if you want.
You probably should learn how to program C++ in general before you get this book, but...
Good luck.
If you are reading the book, and have NO idea what is going, try and download something like C++ for dummies. That will give you a better basic idea on things you will learn off of Sams C++ in 21 days.
Just don't think that you'll become a professional programmer over night. If you want to get good fast, read a LOT of books on C++ and skim through them if you want, just pick up information off of them, and try to program new things as you learn.
You can also find open source programs, and run them, to see how they work.
Anyways, good luck on C++. It's pretty fun once you start getting into it, trust me.