The technology is pretty close right now to build a bipedal robot capable of walking and running with reasonable agility for a "soldier." Machines are already quite capable of operating weaponry and shooting to kill. Even autonomously. But, in order to keep construction and maintenance costs low... it's better to go with a simpler design. Walking is a complicated motion and requires fine controls, fine sensing, and processing power to calculate in real time. So you're going to see a lot of tank-treaded robots, hexapods, snake-like robots, etc. Anyway, the big barrier for your question is artificial intelligence. We haven't quite figured out how our own intelligences work yet, and it took a few billion years for Nature to produce us. AI has a long, LONG way to go. There's no reason you couldn't create a walking, talking, killing machine with today's technology and enough funding... but it'll require a remote operator to sit at a computer and make it's decisions.