Well, if you know the following will be true:
-The file will be changed
-There won't be a file with the same name
You can do this:
SendKeys "%{F4}{ENTER}file1.txt{TAB}{TAB}{ENTER}
This will close the program, it'll ask if you want to save, OK will be chosen, a filename entered and OK chosen again. This is a very unreliable method and will only work on WinXP (small adjustments are required for others due to less listboxes), but it should do for simple stuff. file1.txt is the filename, which will be entered right where it should be. If the file already exists the user will have to manually choose whether to overwrite, and if it's unchanged Notepad will close and everything after Alt+F4 will be sent to the next program which could be a problem, so consider typing and deleting something to avoid this.
[edit] Oh yeah, and on XP you can use Ctrl+S to save - the filename dialog will only appear on an unsaved file!