It depends on how much muscle you would like to gain. If you plan to gain a lot, than it will be hard not to raise your weight, but you can lower your body fat %.
This is what my friend did, he was at 270 pounds, almost all fat. He biked to the gym each day, and back. While at the gym he did a bit of running, and than the rest, just lifting weights. Over the summer he dropped to 240 pounds, and gained some muscle, though I don't think he was eating properly, because he could have gained a lot more muscle, but didn't.
I'm planning on doing that myself, I'm not over weight, I just think it's a good thing to do. It gets your heart pumping, and counts as a warmup, than you have more time to be lifting weights.