<property name="TF" value=""C:\Program Files (x86)\Microsoft Visual Studio 11.0\Common7\IDE\TF.exe"" />
<Exec program="${TF}" workingdir="C:\TFS-Build\Get-App" commandline="get $/Main/XYZ /all /overwrite /force /recursive /noautoresolve /noprompt"></Exec>
Check this page for more details:EXEC Task