GMaps is now capable of providing driving directions, from Google, from a given location to the marker defined on your map.  The default setting within GMaps is to show only the detail data of the markers.  You can easily enable this feature by changing a setting on your map.  To do this, click on the 'Markers' tab when editing your map information.

To the right is a screen image of the tab and its associated page (as of Rel. 1.0).    Just set the "Enable Driving Directions" to Yes and click the 'Save' button.  After this, the next time the map is rendered, click on the marker and the tab should be there.

NOTE:  The screen image provided will change in future release to support additional configurations.