I make precooked hams faily often, I put them in the oven at 325 for about 20-30 minutes per pound. All you're doing to a preecooked ham is heating it, so don't worry about eating raw ham. I put a little water in the bottom of the pan, and make a tin foil tent and put it on top the ham. I have cooked them longer and at a slightly higher heat (like when I'm baking scalloped potatoes to go with it), and it doesn't seem to matter.