That's an excellent book - I have it - but it's really unecessary for this question.
Jacob - you need to use your hosts control panel to setup an FTP account. Write down the information supplied (username, password, etc). Then download any of the free FTP applications available (CuteFTP, FileZilla, WS_FTP, etc) and install it using the info from your ftp account. Go to your site using ftp and point your destination to the folder "wp-content/themes". Point the source folder to the location on your computer into which you have downloaded and extracted the theme you want to use. Just transfer the ENTIRE folder and files to the themes directory for WP and you'll be in business except for setting the folders file permission to 755 so you can make any edits you want.
There is an FAQ in the Codex on this, and whooami has an excellent "hold my hand" video on how to do this step by step.
I understand powweb has some unusual ways of doing things, so if they won't allow you to do this my suggestion is to get yourself a more user friendly host.