DirectRT v2006.2.10, posted July 1, 2006. It's a free update for all v2006 users and includes the new manual and help documentation. You can get it from the main download page: www.empirisoft.com/download.aspx.
You can also get a copy of the manual on its own here www.empirisoft.com/download/drt2006/directrtmanual.pdf
You can also view the interactive help files online here: www.empirisoft.com/directrt/help/_helpcontents.htm