With the inclusion of Autodesk 3ds Max Design 2012 in many of the new Design Suites, there are more people starting to experiment with this product. We thought it might be useful for you to know where the Units settings are to help get you setup correctly.
To customise the default Inch Units, go to the Customize menu > Units Setup.
Change Display Unit Scale to Metric, then click the drop down list to pick Millimetres.
Then click on System Unit Setup > pick Millimetres again.