If you need to register and unregister NCover as part of your build process you can easily use the provided NCover.Registration.exe provided by the NCover installation.

Here's a snippet of a build file:

 <BuildRoot>$(MSBuildThisFileDirectory)</BuildRoot>  
 <BuildToolsDir>$(BuildRoot)\BuildTools</BuildToolsDir>  
 <BuildSolutionDir>$(BuildRoot)\Src</BuildSolutionDir>  
   
 <NCoverRootDir>$(BuildToolsdir)\NCover</NCoverRootDir>  
 <NCoverConsoleExe>$(NCoverRootDir)\NCover.Console.exe</NCoverConsoleExe>  
 <NCoverRegistrationExe>$(NCoverRootDir)\NCover.Registration.exe</NCoverRegistrationExe>  
 <NCoverMSBuildTaskAssembly>$(NCoverRootDir)\BuildTaskPlugins\NCover.MSBuildTasks.dll</NCoverMSBuildTaskAssembly>  
   
 <TestMSTestExe>$(VS100COMNTOOLS)\..\IDE\MSTest.exe</TestMSTestExe  
 <TestResultsDir>$(BuildRoot)TestResults</TestResultsDir>  
   
 <UsingTask TaskName="NCover.MSBuildTasks.NCover" AssemblyFile="$(NCoverMSBuildTaskAssembly)"/>  
   
 <Target Name="TestNCoverRegister">  
           <Exec Command="&quot;$(NCoverRegistrationExe)&quot; //license [KEY]"/>       
 </Target>  
        
 <Target Name="TestNCoverUnRegister">  
           <Exec Command="&quot;$(NCoverRegistrationExe)&quot; //deactivate"/>  
 </Target>  
        
 <Target Name="TestUnitsNCover" DependsOnTargets="Prepare">  
           <MsBuild Projects="$(MSBuildProjectFile)" Targets="TestNCoverRegister" Properties="ForceExecute=1"/>       
           <Delete Files="$(TestResultsDir)\UnitTests.trx" />  
           <NCover  
                     BuildId="$(BuildNumber)"  
                     ToolPath="$(NCoverRootDir)"  
                     TestRunnerExe="$(TestMSTestExe)"  
                     TestRunnerArgs="/testcontainer:&quot;$(BuildDir)\MYAPP.UnitTests.dll&quot; /resultsfile:&quot;$(TestResultsDir)\UnitTests.trx&quot; /runconfig:&quot;$(BuildSolutionDir)\LocalTestRun.testrunconfig&quot;"  
                     CoverageFile="$(TestResultsDir)\UnitTestCoverage.nccov"  
           />  
           <MsBuild Projects="$(MSBuildProjectFile)" Targets="TestNCoverUnRegister" Properties="ForceExecute=1"/>  
 </Target>  

Some notes about this build:

• NCover is not installed in the Program Files directory, I like to keep all files required for a solution as part of the source so all of my "tools" are kept in \BuildTools.  This way if a new developer checks out the solution root they don't need to install any additional software (apart from the core things like VS and SQL Server etc)
• You'll notice I'm not using Call task or DependsOnTargets to run the register/unregister targets, I'm using the MsBuild target to call the same build file in order to execute the same MSbuild target twice.  The reason I do this is because I have another integration test target that dopes the same thing as the unit tests but on a different DLL, so I want to be able to call the targets individually or together as part of a commit build 

Today I needed to use the TFS API to get the last successful green build info from TFS so I thought whilst I'm still learning PowerShell I'll give it a go in that.  Anyway here's what I came up with, I could have condensed the lines but whilst I was debugging in PowerShellGUI (which is REALLY good for PowerShell development!) I wanted to see what each method returned.

 [void][System.Reflection.Assembly]::LoadWithPartialName("Microsoft.TeamFoundation.Client")  
 [void][System.Reflection.Assembly]::LoadWithPartialName("Microsoft.TeamFoundation.Build.Client")  
 [void][System.Reflection.Assembly]::LoadWithPartialName("Microsoft.TeamFoundation.Build.Common")  
   
 $tfsCollectionUrl = "http://SERVERNAME:8080/tfs/COLLECTION"
 $server = new-object Microsoft.TeamFoundation.Client.TfsTeamProjectCollection(New-Object Uri($tfsCollectionUrl))
 $buildServer = $server.GetService([Microsoft.TeamFoundation.Build.Client.IBuildServer])
 $buildDetail = $buildServer.QueryBuilds("TEAM_PROJECT", "BUILD_DEFINITION_NAME") | where { $_.BuildDefinition.LastGoodBuildUri -eq $_.Uri } #| select BuildNumber
   

$buildDetail will contain an IBuildDetail object as described here: http://msdn.microsoft.com/en-us/library/microsoft.teamfoundation.build.client.ibuilddetail.aspx