<p>So after installing NUnit, the assemblies (<code>nunit.framework</code>, etc.) now appear in the <code>References &gt; Add Reference</code> dialog, but they're not in the <code>%WINDIR%\Microsoft.NET\Framework\v2.0.50727</code> dir and there is no <code>NUnit</code> registry entry for the Assembly Path <code>(i.e. HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\.NETFramewokr\AssemblyFolder)</code>.</p>

<p>There's also no automatic entries created in the project properties Reference Paths for the <code>NUnit</code> install directory.  How the heck are they appearing in the "Add Dialog"?!?!  I thought the mentioned way were the only ways assemblies could appear in "Add Reference".</p>

Strange, [HKEY_CURRENT_USER\SOFTWARE\Microsoft.NETFramework\AssemblyFolders] should be the only thing driving this.
Perhaps this snippet from
this page
is relevant?
If you install the .NET Framework 3.0 Service Pack 1 (SP1), the following registry subkey is added:
```
```
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\.NETFramework\AssemblyFolders\v3.0
```
```
If you install the .NET Framework 3.5, the following registry subkey is added:
```
```
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\.NETFramework\AssemblyFolders\v3.5
```
```