If you are severely overweight and are needing to get your weight down for health reasons, then by all means do as much cardio as you can until you get your weight down to something healthy. If you want to be the strongest powerlifter you can be, then cardio (running, biking, etc.) is not a great idea, but if you are 100 lbs overweight then you need to get rid of that weight so you can be in good enough condition to train properly and have some level of health.
That being said, if you are only 20 or 30 lbs overweight, just hit the weights hard, clean up your eating, and everything will probably take care of itself.
And before everyone jumps on this one, I am fully aware that I am 50 or 60 lbs overweight according to the government charts. That is not what I am talking about. If you are around 15 percent bodyfat, then you are probably not overweight (IMHO) whether you weigh 150 or 350, or anything in between. But if you are 30 percent bodyfat, you are overweight regardless of what the scale says. I have seen fat 140 lb men. They are the worst of the worst, I have heard them referred to as "skinny-fat" meaning no muscle, no mass, but what little is there is all fat.
And if you have trouble walking or running, and for some reason cannot either buy, find or make a sled, then swim. Swimming is great, no impact, burns lots of calories, pretty fun to do, and the higher bodyfat you have, the easier it is to float.
B.