I discovered a way to make quite decent frozen yoghurt. You'll need a food processor (maybe a blender would work). Put your yoghurt of choice in the appliance and turn it on. Then feed frozen fruit (i like to use frozen cherries) into it. You should get a sludge of fairly small crystals. Add any syrup you want to use to sweeten it and put into an airtight container and freeze. The ice crystals should stay nice and small, keeping the product pleasantly smooth.