Download the disk image - Download
Copy DataTank.app into the /Applications folder
If you don’t have a license, click on the “Send e-mail” button in the window that pop’s up. Wait for the response, which should arrive within 24 hours. It might be quicker.
You get an e-mail back with the registration key. This is a link that will launch DataTank and enter the information.
Most mail programs will allow you to click on the link in the mail message and that will handle all of the rest. If your mail application does not do that, copy the link into the URL field in Safari and hit return. Note that you have to have launched DataTank at least once on that machine in order for the system to know how to deal with the URL.
In the help menu there is a link to a sample file directory on the web site. There are also links to help documents, a way to sign up for the discussion board and send e-mail with a question.