You can download and install the DITA Open Toolkit from SourceForge.net.

Source Forge has a Home Page for the Open Toolkit.

The instructions on how to install and use the OT are maintained by Anna van Raaphorst and Dick Johnson as the DITA Open Toolkit User Guide. Note that there multiple packages available for the DITA-OT; if you are trying out the toolkit for the first time, you should use the "full" package, which is designed for easier evaluation. The User Guide contains information on the different packaging options.

Don Day maintains a DITA Open Toolkit Resources Page.

An online step-by-step tutorial on installing the OT is provided by Lone Dita.

If you find installing the OT too difficult, consider a free running version of the DITA Open Toolkit provided as an online software-as-a-service by the DITA Users organization. There you can have an online workspace folder with DITA docsets from IBM and Comtech Services. Edit the files and build them as web (XHTML), print (PDF), and Help (Eclipse). All your work can be browsed on the web by your colleagues as a portfolio of your DITA work with the OT.