I'm using a program called Mobile6, it's an EPA issued program which calculates emission results for cars, etc.
anyway, the program uses a DOS interface and requires an input file with the extension ".IN"
this input file is always compiled in notepad. So, when I go to save the file, I save it as whatever.IN, not as .IN.txt or anything, but of course notepad adds its .txt extension. I can't get XP to stop associating it with notepad.
even if I change the folder options of that file to always open with Mobile6, it still thinks it's a .txt file. I've used another XP Pro PC where when you saved the file, it appeared as whatever.IN.txt and you could simply rename it and remove the .txt part, and then XP wouldn't associate it with any particular program.