When you create a burn folder in Tiger (which you do by either choosing New Burn Folder from the File menu or from the Action menu [that’s the button with a gear icon on it in Finder windows]), if you look inside that folder, you won’t see your original files. Instead, you’ll see aliases to the originals (you can tell they’re aliases because they have a little curved arrow on them). But don’t let that throw you — when you do finally click the burn button (in the upper right-hand corner of the burn Folder’s window), it actually gets the original files and burns those to disk, so you don’t have to worry about having a CD full of aliases pointing to files you no longer have.
So why all the aliases in the first place? Because it points to your files (rather than copying them into the folder), which makes burning discs much faster than in previous versions of Mac OS X.