Version 2.0 is currently only available to existing license holders, as it completes it final testing phase before public release. (Early Adopters program)

If you are not yet ready for Isadora 2.0, or just want to test the most recent version, you can download the pre-release here: http://troikatronix.com/download/isadora-pre-releases/
Although it will say 2.0 in the splash start up screen, it is only when you purchase a license or a license upgrade to 2.0 that the full feature set of 2.0 is unlocked. In the meantime you will be working with a beta version that has the latest bug fixes, but without the new features unlocked.

If you are a total newbie (welcome to Isadora!) you may want to consider working first with a demo version of the standard release, since it matches the pdf manual tutorials and existing tutorial videos.
Standard Release v1.3.x: http://troikatronix.com/download/isadora-download/
Be sure to download the manual from the 'Related Downloads' section, also run the installer for Pete's FreeFrame plugins, and visit the online video tutorials available via the help menu, all of which is available with the free demo version.

Available for download today.  http://troikatronix.com/download/isadora-pre-releases/

More info here on the Isadora Forum from Mark Coniglio
http://troikatronix.com/troikatronixforum/discussion/1391/new-beta-version-1.5.3f25-everyone-should-upgrade