Before using AccUnit you have to install SimplyVBUnit 3.0 (project page of SimplyVBUnit at sourceforge).
You will find the setup file here: SimplyVBUnitSetup.exe.
*** 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.