I'm not coming this far with you, only to see you beaten by some software. You control the software remember, it's not the other way around.
NetObjects Fusion likes to save sites in its own directory, with the .nod file extension. Let it do that - don't try to change the default folder. When you save a site for the first time, using the file/save as command, NOF will present you with a 'users' folder, and all you have to do is choose a name for the site - call it anything, it doesn't matter. Then, as you work, you can save your changes by clicking the 'save' icon. Do this often, don't work for two hours and then see your machine crash on you, losing all your work.
If you shut down NOF without remembering to save, it will remember for you, and will back up your changes to the default folder. Give it a try, and don't let it beat you.