Our house is over 100 years old, too. The upper sash was fixed while the lower sash went up and down and was held up by a stick. Since I wanted to save as many of the old panes as possible, here's what I did.
1. Used a putty knife to pry off the trim holding the sashes in the opening.
2. Took the sashes out (we had storm windows to keep out the weather)
3. Laid the sash on a large work table that gave me plenty of room to work.
4. Chipped out the loose glazing
5. Use a heat gun to soften the remaining glazing. Care must be used to not heat the glass too much or it will crack.
6. Remove remaining glazing.
7. Remove the glazing points.
8. Lightly tap the pane from the other side to remove.
9. Clean glazing off the pane.
10. Sand sash where the pane sits to bare wood and prime (oil based primer).
11. Lay bed of glazing for the pane to sit on, lay pane on glazing compound and lightly press to set and install glazier's points.
12. Lay bead of glazing compound around pane.
13. Form with putty knife
14. Clean off excess from both sides of pane.
15. Allow overnight to cure and prime and paint.
This is an overview, if you want details about any step, just ask.
This is a tedious process requiring lots of patience or glass will break and leaning over the table hurts the back, but it beat installing modern windows.
