That should be the correct program, but if they're .dsk files for the Apple II, you can't mount them like normal floppies. Those are intended to be used with an emulator or to be written to a floppy using a program like ADTPro.
First, try opening Disk Copy, then opening the .dsk from through the File Open menu. If you don't have the appropriate extensions, Disk Copy may fail to open the file if it is double-clicked or dragged onto Disk Copy.
Additionally, if the .dsk file has lost its Resource Fork, it won't mount on a Macintosh using Classic (Pre OS X.) You'll have to mount it on an OS X machine. Hopefully you have a Mac with both OS X and OS 9 running in Classic mode. Mount the .dsk file under OS X, then use Disk Copy under OS 9 to convert the volume back into a .dsk file, then make sure you zip or stuff the file using a Classic application (like DropStuff) to preserve the Resource Fork. You can now copy it back to an older Macintosh.
There might be an easier way, but I've never had luck getting OS X to play nice with Resource Forks.