For others who may need the information and don't realize it from the XML snippet above , there is a RequireCheckout property available (True=Files must be checked out, False=Checkout not required)
i.e. where listService is a connection to the WSS Lists web service
System.Xml.XmlNode listInstance = listService.GetListAndView("yourListName", "");
listInstance.ChildNodes[0].Attributes["RequireCheckout"].Value;