You can use the calculator on this site to see what your weight maintenance target for daily calories is, then if you are lifting weights try adding a couple hundred calories extra per day. You can then check every couple weeks using a caliper or something similar to see if you are gaining fat as well as muscle, if you are then you can tweak your foods. As far as slowing your metabolism, well you could stop lifting weights and do no cardio, just sit on the couch every day. Then all teh calories will turn into fat, but I don't think that's your goal.
