I don't think you can rent an iTunes extra.
When you buy it, yes, you can look at all the data inside. On Windows, its simply a folder with a .itlp or .ite (I think) extension. Just open it up like you would any other folder. On a Mac, I believe you have to give it a .zip extension or something of that nature.
Apple has also posted sample iTunes LP and iTunes Extra files for download on their website so you can test them out if you are interested in making your own.