You didn’t specify your operating system. This works with XP.
Open My computer and go to the location where the .dss file(s) reside.
Right-click on a .dss file.
Chose Properties.
On the General tab, you will see “Opens with” and a [Change] button to the right. Click this button.
Select the program which you wish to have Windows use to open .dss files.
[OK] your way back out.