DARPA's Budget Item Justification Sheet contains goodies that seem right out of the pages of science fiction, like laser-guided bullets. The goal appears to be to "enable low-cost, high performance guided projectiles" that take advantage of "guidance and targeting systems." While the idea of a laser-guided bullet conjures images of soldiers marching across fields, spraying ammo that never misses, the report mentions that the technology is intended to be used by Special Forces and Army Sniper Teams. So, boiled down, we're talking a bullet that's going to be fired at long range by a sniper and be able to adjust its trajectory mid-flight, as to have a better chance of hitting the target. Sounds like the military just doesn't want to train their snipers. Laser-Guided Bullets: Pentagon Pursuit [WIRED]
The problem with a conventional bullet is that, due to rifling, they are spinning at 150,000+ RPM when they come out of a barrel (do the math...1 in 12 rifle twist at 3000+ Feet per second).
There is no way to implement a guidance system in such a small package (150 grain or so) that can overcome the inetial/gyroscopic force of the bullet spinning that fast. It would have to be a smooth bore rifle with a very, very unconventional design to work.
In other words...it is not a bullet out of a gun design that you are thinking of. More along the lines of a modified grenade launcher.