OK once you find the file just right-click and "Send to:" 3.5 floppy.
If you are talking about the exact file that you saved from DS, you need to find out where they keep them. You best bet is to "find" the file extension. Lets say the file is "mysuperfastgn.dss" go to start->find (or maybe search) and search for "mysuperfastgn"