It's impossible to 'force' a user to do anything - they could always disable the macro or, even if they let it run, it's difficult preventing them cancelling out of the dialogue or forcing the macro to crash. Depending on what you're doing, you could, however, encode the macro to do its own 'Save As' without user involvement. See, for example:
http://www.techsupportforum.com/foru...er-694900.html
In any event, from your description it seems you should be using a template, not document. Double-clicking on a template creates a new document that can only be saved via Save As.