It will work as car sat nav too, not anywhere near as good as TomTom, but it'll get you there. No voice as you say.
You don't need one, but its great to just ride without thinking about the route you're taking next. You just ride till it beeps, look down to check the direction, and carry on.
It doesn't come with any software. Something like MemoryMap is very handy to plot routes on then save to the Dakota, but there are free ways to do this I think, and theres loads of GPX files about on the net ready made.