Doors and Windows - doorhardware replacement - old hardware

Our new home has very old (think 1920) door hardware. unfortunately the previous tenant/owner did not take care of them and we will be selling to a salvager in our town. We want to replace them, but we want to strip and restain the doors (gorgeous hardwoods). Can anyone get me started on what measurements to take and exactly what these things mean?
I am a young first time home owner. I have stripped and refinished furniture in the past so I can do this, but hardware is a whole new world to me.
Thanks!
New home owner.

What are you selling to the salvager?
What are you replacing it with?
Is it mortised or cylindrical?
And why are you not repairing?

I believe it is mortised, I am not completely sure what those terms mean. We are selling the knobs and interior components. We are not restoring given the amount of work that would be involved here and missing pieces to many of sets. They are covered with years of paint (I would say at least ten coats of paint on these suckers). Many of the sets are no longer matching, springs seem to be missing, etc. This is my first encounter with older door hardware.

If you are going to replace the hardware you might find what you are looking for here and other places: http://www.houseofantiquehardware.com/index.htm