Yellowbird, somehow I have missed your post.
I have attached the file to the placeholder using CTRL + SHIFT + ALT + A
You can also put it to the support folder. The support folder has to be placed along with your design file and have a specific name. For example, if your designs filename was homepage.xar the folder has to be named homepage_xar_files, if it was homepage.web it would be homepage_web_files instead.