How to Save Energy When You Fix Up the Outside of Your Not-So-New House Retrofit Best Practices Guide, January 2004, Oak Ridge National Laboratory This is a 30 page downloadable pdf/. Some good information about storm windows and low e glass as compared to double pane windows.
Creating Windows of Energy-Saving Opportunity Shapiro & James, Home Energy Magazine, Sept-Oct 1997. Removing and replacing your old windows may not be the best idea. View the article on line.
What Replacement Windows Can't Replace The Real Cost of Removing Historic Windows Walter Sedovic & Jill H. Gotthelf, APT Bulletin, The Journal of Preservation Technology, Vol 36, April 2005, pp 25-29. 5 page downloadable pdf.