I take it that with "histogram" you are not plotting all 800 data points, but an aggregation of the data.

You can use a combination chart with an XY chart plotted on the secondary axis to create lines. The exact steps would be easier to describe if you could post a sample file and also let us know your Excel version, since there are some differences. Also, it would help if you already have formulas for the mean and median calculation in place.

cheers, teylyn