By default the NUnit installation program places all of the files into the C:\Program Files\NUnit 2.6.1 directory. In the installation directory there are up to three sub-directories, depending on what the user has chosen to install: bin, doc and samples. Source code is no longer provided with the binary installation package but may be downloaded separately.
The installation program places a number of shortcuts in the start menu, which run NUnit under .NET or Mono, depending on what is installed on your system. For NUnit 2.5, the gui only runs under version 2.0 of the CLR, although tests may be executed under other versions using a separate process.
NUnit's own tests are available as an installation option. If you installed the tests, you may verify that the installation has worked successfully by running the NUnit gui and loading and running NUnitTests.nunit. All tests should pass.
Additional tests are included with the samples and in separate assemblies used as data by the verification tests themselves. Failures or not run conditions in these tests are intentional.
You may build NUnit from source using one of the Visual Studio solutions or the NAnt script. In either case, an output directory is created, which contains all files needed in the proper relative location. Just copy this directory to a permanent location and create shortcuts if desired.
NUnit's .NET 1.1 support is packaged as a separate download. It may be installed independently, in which case it provides only a restricted version of the console runner, or as part of the overall NUnit installation. When used together with the primary NUnit installation, it allows you to run .NET 1.1 tests under the Gui. For complete functionality, install in the same disk location used to install NUnit itself.