At this time (mid-October 2007), Version 3 of the Guidelines for Image Creators (formerly just "the Guidelines") is available only as a set of web pages, not yet in PDF. But a PDF of the Quick Guide is available.
The PDF version of the complete Guidelines is still in process. If you can't wait, the Version 2 file is still available.
Historians can request version 1 by writing to info@updig.org.
The PDF edition of the Guidelines for Image Receivers is also in preparation. The document will be posted here when it is ready.