Ok, easy way, if you haven't tried this yet.
Right click on the *.bb file in Windows Explorer. There should be an option "Open With >" Mouse down to that, then in the popup menu, click on "Choose Program" Select Blitz from the program, or navigate it from the "Browse" option. Make sure "Always use etc..." is selected.
It should use Blitz from then on.
Right click on the *.bb file in Windows Explorer. There should be an option "Open With >" Mouse down to that, then in the popup menu, click on "Choose Program" Select Blitz from the program, or navigate it from the "Browse" option. Make sure "Always use etc..." is selected.
It should use Blitz from then on.