To thicken up a stew, use mashed potato flakes. It gives you that potato flavor. Instead of boiling your meat and veggies in water, use beef broth. Great stuff.
I always make my beef stew by almost cooking the beef in sauce, etc and then adding the vegetables and having them cook in the liquid of the stew. I never find it necessary to thicken the liquid because there isn't that much and I would use cornstarch because I do not keep instant potatoes around the house.