Saw this on RG:

The "IPTC Core Schema for XMP" version 1.0 specification was approved by the IPTC in 2004 and is being released publicly on March 21, 2005. From the IPTC site you can download the custom panels for Adobe Photoshop CS, as well as a full package that includes a comprehensive user guide to these panels, example photos with embedded XMP information, the specification document, and an implementation guide for developers.

Check out the tutorial video as well here (QuickTime needed)