Your topo is correct regarding the location of the Diving Board. It is a formation at the top of the Porcelain Wall, the "little brother" of Half Dome. It can be reached by using the approach to the Snake Dike route on Half Dome, and then traverse across from Snake Dike. Info from an old climbing route guide to Yosemite.
A number of years ago the Porcelain Wall was scoured by a major rock fall, so I don't know the condition of the top of the route or if the "real" Diving Board was damaged. The route to the Diving Board is definitely NOT a tourist hiking route!
The formation on Half Dome that some refer to as the diving board is actually called The Visor. But I suppose it can be called whatever suits a person...
In the photo below from supertopo, the Porcelain Wall is the blank looking wall to the right of the Southwest face of Half Dome. The Diving Board is the overhanging formation at the top of the wall.
http://www.supertopo.com/photos/0/50/126555_21282_XL.jpg
