If the book is Teach Yourself Perl in 21 Days by Laura Lemay, it's a perfectly good way to learn perl. The 21 days part is decieving: you could only devour the book and do all its exercises in 21 days if you did nothing else except sleep and eat. Even then, you wouldn't get enough practice with all the things you learned.

I got through the first few chapters in a few weeks, and then referred back to the book when I wanted a tutorial on, say, regexes, or the debugger. That, the manpages, and Perlmonks were all I needed to get a pretty solid foundation of the language.

If it is this book, then it has a fairly extensive chapter and apendicies about how to obtain and set up Perl on Unix, Windows, and MacOS. The only thing that makes me suspicious is that jjohnson says "I have downloaded \"Learn Perl in 21 Days\"". This either means that I'm thinking of the wrong book, or that jjohnson just downloaded the code listings from the book's site and didn't read the book. That's usually not a good way to learn Perl.

Tell us when you get it working, jjohnson.