Windows Explorer can be set to display thumbnails for material (.mxm) and scene (.mxs) files.
Normally, this feature is enabled during the installation of Maxwell, so the user doesn't need to do anything but here is the "fine detail" in case you need it.
thumbplug_mxm.dll and thumbplug_mxs.dll (Windows Dynamic Link Libraries) are supplied to handle this functionality. They must be registered in Windows to enable the functionality, or un-registered to remove the functionality.
To Register
regsvr32 thumbplug_mxm.dll
regsvr32 thumbplug_mxs.dll
To Un-Register
regsvr32 /u thumbplug_mxm.dll
regsvr32 /u thumbplug_mxs.dll