This is how I would go about it...
Load up Windows Explorer, and select 'Folder Options' from the Tools menu.
Now select the File Types tab, and look for the DBA extension, select that and press the 'Advanced' button.
Now you should be able to add a new option to start a new DBA, I'm at work right now so can't test this at all, but...
Click New, then for 'Action:' specify '&New', and specify the location of your DBPro editor.
No idea if this will work, but you can't do any damage by trying this, I see no reason why it won't simply load up the editor with a blank project. Personally I just make a new text file then rename it to .DBA, and load that up to get started.