There is a third way which I prefer. You can also use devenv.com. It's faster than NANT, doesn't require NANT bins and works on any machine with VS installed. You also avoid possible errors with MSBUILD (http://support.microsoft.com/kb/964125).
Just use %path_to_devenv.com%\devenv.com "%path_to_sln" /<buildoption> BuildConfig
In my case it's
%ProgramFiles(x86)%\Microsoft Visual Studio 10.0\Common7\IDE\devenv.com "C:\Projects\XYZ\xyz.sln" /rebuild Debug
This way it's guaranteed that your project will be build exactly the same way as it's being built in Visual Studio.
EDIT:
Now that we know how how much there is to do, I'll try to give an outline how you can setup the whole system for automated build controll.
- Set up your repository (I hope this is already done - tell me if not)
- Install and set up Jenkins (https://wiki.jenkins-ci.org/display/JENKINS/Installing+Jenkins) including users, ClearCase-Credentials, plug-ins for ClearCase, MSBuild, etc. (all of them can be found in the Jenkins plug-in interface) - this is the biggest peace of work
- Create and set up a new project in the jenkins interface (name, working directory, etc.)
- Tell jenkins to use source code management (e.g. subversion module), enter the ClearCase repos to use, set the desired behavior of the source code management
- Set a build trigger (I recommend checking the source code management each minute: * * * * *)
- Add a build step and select "Build a Visual Studio project or solution using MSBuild" - this option should appear after installation of the MSBuild plugin (https://wiki.jenkins-ci.org/display/JENKINS/MSBuild+Plugin)
- Set the path to the .sln file (you have checked it out from your repository)
- Add more optional arguments if desired (eg /p:Configuration=Release or Debug or whatever http://msdn.microsoft.com/en-us/library/vstudio/ms164311%28v=vs.110%29.aspx)
- Play around untill it works
Btw., I recommend to put all external dlls into your repository.