More specifically, for Windows users, goto the NUnit download page and download the most recent stable version of NUNIT for .NET 2.0. As of February 2010 this is the NUnit-22.214.171.12445.msi file (a Windows installer file). You can also get this file directly from here.
Mono users on Linux probably already have an installation of NUnit. According to the NUnit documentation, Mono 1.0 through Mono 1.9 include NUnit 2.2. Try calling the NUnit console runner named nunit-console from your shell. Please be aware of the version you are running. The newest stable version of NUnit is 2.5.3 (as of February 2010). Mono users are recommended to use version 2.4.8, however. See also the release notes.
There is no solution to this exercise