What! You remind me of a man calling the customer support and asking where to download the Internet and whether he would need a larger floppy disk
I saw the website and each tech tutorial seem to be a directory of the w3schools.com site (like *www.w3schools.com/xhtml/default.asp). In the offline explorer that you have downloaded, you must have an option to create a new project. In that specify the starting url as "www.w3schools.com/xhtml" for downloading xhtml related content. Also make sure you get only the type of contntet that you need. For example, you won't need swf or gifs unless the tutorial uses it to illustrate a point.