Before using AccUnit you have to install SimplyVBUnit 3.0 (project page of SimplyVBUnit at sourceforge).
You will find the setup file here: SimplyVBUnitSetup.zip.
*** IMPORTANT *** As of November 2012, on the SimplyVBUnit's project site, there is the version v4 of SimplyVBUnit available. That version is not compatible with AccUnit. Thus, make sure to use the link to SimplyVBUnit 3.0 provided above.
You may start the download of AccUnit here: AccUnitSetup.zip
Start you installation with Setup.exe. The setup attempts to install the Visual C++ 2010 Runtime. If you encounter problems while that part of the setup (typically because there is already a newer version of the C++ Runtime on your machine), start the installation with the msi-file.