file ext dmg.sit and quicken

Just new mac user trying to make it 'purrrrfeccct'

I downloaded an app that has .dmg.sit file extensions. Double clicking brings up a widget asking which app to open it with. What is dmg.sit? The app is quicken and I read that rosetta was supposet to automatically open and run it. I searched and can't find rosetta.

Now macbook pro comes with quickbook nue, which is registered, could one some how conflict with the other?

Mike