Download v2.1: http://troikatronix.com/download/isadora-download/
However, it is strongly recommended that before you dive into it... that you actually take a few minutes to study the release notes. Some of the changes are much more than cosmetic! If you take the time to understand the way that video can now be handled on the GPU (graphics card) instead of the CPU (computer processor) for instance, you can significantly improve the efficiency of playback of multiple HD video clips and live camera feeds. But in order to achieve that you should study the release note's recommendations for changes to the recommended video codecs for compression.
v2.1 Release Notes: http://troikatronix.com/isadora-2-1-release-notes/
An update to the older version 1.3 Isadora User Manual is underway, scheduled for release with v2.2 in late December.
The next release is scheduled for the end of the year... containing serious new tools for the ambitious video artist! So keep an eye on the user forum and troika website around that time.