Maurine:
Take a look at
http://www.getbodysmart.com/ap/muscularsystem/thighmuscles/posteriormuscles/bicepslonghead/tutorial.htmlto learn about the hamstrings
Also, for the knee
http://en.wikipedia.org/wiki/File:Knee_diagram.svg (anterior view, from the front)
http://en.wikipedia.org/wiki/File:Gray351.png (lateral view, from the side)
and
http://en.wikipedia.org/wiki/File:Gray352.png (posterior view, from the back)
see if those pictures allow you to describe the problem more precisely.
Also, do you happen to know which hamstring muscle was involved?
I actually do have something similar. I get a click when the semitendinosus/semimembranonsis tendon goes over the tibia. I used to think it had some special significance (as in causing some kind of big inefficiency when running), but do not any more.