When I open DDSWMM it asks me to specify the path of the the file I want to open. Do I have to create the file with Notepad and then rename it to .dat before opening it?
No, you don't need to create a .dat file with Notepad. The program is asking you to open an existing project. If you don't have a DDSWMM project, press Cancel and you should be able to create a new one. I suggest you contact the support team for further information. You can get in touch with them using [email protected] email address.