Hi Demo Man,

There is a free application you can download from Apple to create your Apple Loops. You can get it here:

http://developer.apple.com/sdk/

It's called "Apple Loops SDK 1.3.1 SDK (DMG)."

Open your audio files in this app and start tagging all the meta data. IMO, these are the most important fields to fill out:

File Type (looping or non-looping)
Key (if applicable)
Time Signature
Genre
Instrument and Sub-Instrument

Then click on the "Transients" tab and make sure the transient markers are placed correctly. This app does a pretty decent job of figuring them out, but to double check, I like to lower the preview tempo of the loop down 15-20% of the original tempo. If a transient marker is misplaced, it's most often noticible by a "flammy" effect when you listen to it.