heres_luck has a great post on making squash soup here (http://www.livejournal.com/users/heres_luck/140093.html). I have made the Thai curry variety using butternut squash and adding some ginger, and it was awesome both times. With the ingredients you've got, I'd think you could modify any of those recipes, baking the sweet potatoes along with the squash and adding both to the pot at once, for example. Good luck!