I started a diet a short time ago and have droped from 229 to 211 lb. If I were to start a very rigorous weight lifting regiment would it still be possible to loose weight but gain muscle mass at the same time?

Yes it's possible, but pretty difficult. If you are losing weight the right way (not starving yourself) and maintain a solid diet while starting a routine, you should see some results. It may not be a lot of muscle mass, but some muscle at least.

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.