The Team Foundation action enables only the fields that are valid for each command. You need to map a working folder, which can be done from the VSTS GUI or from VBP via the Workfold command (See the 'new workfold mapping' subroutine step in the Team Foundation.bld sample
http://www.visualbuild.com/Manual/teamfsample.htm), followed by a Get command to get to the current working folder.