Im not sure what kaplan cd you are talking about: There is a path one and then one that comes with the qbook?
The one that comes with the qbook is a mock test with answers similar to the qbook but the qbook has "tests" on each subject.
i.e. the qbook is like the NBME tests while the cd is like step 1
still invest in qbank before any of these...it is much more useful
hope this helps