QTL syntax

The href="URL" will open when the QuickTime .qtl file is clicked on.
<?xml version="1.0"?>
<?quicktime type="application/x-quicktime-media-link"?> is required in any .qtl file. It gives the XML instructions.

It's neither.
It is a URL. In URL syntax "book" is a folder found in my iDisk Sites folder. Inside the book folder is an "index.html" file (no quotes). A page named index.html does not have to be included in a URL as it is read by default.
The .qtl file (in this XML format) points to the "src" (source) QuickTime .mov file. That file can be anywhere on the Web and the .qtl file doesn't have to be in the same location as long as you use the complete URL to the .mov file.

Let's back up a bit so you understand the steps.
Create a QuickTime .mov file and upload it to a server.
Create the .xml file in any plain text editor. Change the URL in the "src" tag (no quotes) to point the file you uploaded. Use a "complete" address (starts with http and ends in .mov).
Edit the other tag code if needed to add other features. Add a "href" URL if you want to open a Web page with a click on your .mov file.
Save the text document and append the .qtl file extension. Upload this file to your server.
You can add this "text based" link directly in your Web page code and a page visitor will be able to click on it to download the .qtl file.
When the .qtl file (very tiny in file size) is downloaded it will launch the QuickTime Player app and it will begin to download the "src" file. The other features such as full screen will be "forced" on your QuickTime .mov file so be sure to size it appropriately for that display size. You don't want a 320X240 size pushed up to full screen.
A "href" link in the .xml file can be used to open a Web page when a viewer clicks anywhere on the QuickTime display window (even in full screen mode).

http://homepage.mac.com/kkirkster/LemonTrees/LemonTree.qtl

Test my file to see how things fall together. You can open the downloaded .qtl file in plain text editor to see the exact same code used in my example above.

You have an iDisk and it becomes your file server. You need only learn how to use it.
iDisk has more than a few ways of getting your data into Web pages or directly to your visitors.
In my example you'll notice two "hand made" Web pages (my book page and the Lemon_Trees page) and the text based .qtl file is a combination of both.
To share these files requires they be uploaded to a Web server. Your .Mac account and iDisk are just that. You can upload to iDisk by using the Finder and drag and drop (no need for iWeb).
If you look at the folder structure of your iDisk you'll quickly figure out the URL syntax for linking files. It goes something like this:
Place a file into the Sites folder of your iDisk and the URL syntax works this way:
http://homepage.mac.com/username/foldername/filename.fileextension (note that the Sites folder is not part of the URL as it is read by default).
Place a file into the iWeb/Sites folder and it uses a different URL:
http://web.mac.com/username/iWeb/foldername/filename.fileextension
This is a different URL syntax because of the way Apple servers direct visitors to your pages but it's the same iDisk. Again, the Sites folder name is not used in the URL as it is read by "default".
Place a file in your "Public" folder and the URL syntax changes just a bit more:
http://idisk.mac.com/username-Public or a frequently unused syntax of
http://homepage.mac.com/username/.Public/foldername/filename.fileextension
The same syntax can be used for some of your other iDisk root folders (Music, Movies and Pictures).
Sounds complicated but it's really very simple once your know the URL syntax.