From the Mars Direct plan:
The same equipment could be used to establish a lunar base - in fact it could be tested comprehensively on the moon before committing to the Mars expedition. In the lunar scenario the Ares booster could launch a 59 tonne payload consisting of the standard Habitation Module with a Lunar orbital capture and lunar descent (LOC/LD) stage. The LOC/LD stage would land the Habitation Module on the Moon. A crew could then be flown to the Moon using an ERV with an LOC/LD stage. This ERV used only the second stage of the Mars ERV for Earth return direct from the lunar surface.
So you'd need a LOC/LD stage for the Hab module, and remove the folding heatshield. As for the ERV - well, in our version of Mars Direct we don't launch the Ares booster manned. So I'm not sure how that would work. The only reason to send an Mars Direct ERV to the Moon would be for test for a Mars mission - otherwise it would be overkill.