When I execute delphi 2009 project using MSBuild command line, output always goes to C: drive
C:\\MyProjects>MSbuild \"C:\\MyTestProject\\Test.dproj\" /t:
I know the docs say otherwise, but try OutputPath instead of OutDir.
For Delphi projects you need to use DCC_ExeOutput to specify where the EXE should go.
C:\MyProjects>MSbuild "C:\MyTestProject\Test.dproj" /t:Build /p:DCC_ExeOutput="C:\Output\bin\"
Take a look inside Test.dproj for any other options you might want to specify.