The following list of suggested steps may assist you in removing a window from its wooden frame. Obviously, you are working with very old materials, and not everything is predictable in this situation.
1. Use a sharp knife and lightly cut all the edges where the paint joins onto the outer lead on the front of the window (this is the opposite to the side with the putty surface).
2. Place the window with the "putty" side up. If the window is large or delicate, place a book or magazine under the glass centre to help support it from sagging.
3. Locate the edge of the putty and the wood frame. Once done, use a hammer to drive the tip of a wood chisel approximately 3/16 of an inch into the wood (just beside the putty) and twist the chisel to break the wood and pry out the putty. Be careful not to pry against the glass. This step takes time!
4. Once all the putty has been pried out, look along the edge for nails or tacks that go through the lead into the wood. They are usually in the corners and along the sides where there are juctures of the lead. It is easiest to use wire cutters to pry out these nails.
5. Rather than try and pry the window out of the frame, I find it easier to cut the frame itself at one of its joints. Use a hand saw and cut through the frame near one corner. Once cut, just gently pry open the frame and the window will be easily freed up.
Sometimes, an accident will happen (typically a crack in an outer pane of glass). If this happens, you should check directory services and the like to see if there are any stained glass studios in the nearby towns/cities that might be able to do the necessary repair work