Currently, there is no install script, but the .net platform allows for simply copying files to install an application.
Unzip the source archive. Simply copy the dll's to a directory of your choice (I suggest a directory where you maintain your assemblies.) and you are ready to go.
When working on a project that you wish to include the testing framework for, simply set a reference to the dll's (dotunit.Framework.dll, in particular) and follow the instructions in the tutorial.