Unless I've misunderstood something, you wouldn't travel back in time as you reached lightspeed.
When stationary, a body travels through time at a rate of 1 s^-2 (ie. one second per second) relative to the rate of the universe. Since the Earth is moving at a significant speed, the rate is different on Earth, but since we are all moving at about the same speed, the difference between any point on Earth is negligible.
However, as you speed up, the rate you travel through time falls, and you experience time dilation. You would not notice this while your were onboard your transportation (which for the purpose of this post I am going to assume is a space ship, or something similar,) since your spaceship is moving at the same speed as you are, and is subject to the same time dilation. It is only when you returned to Earth that you would notice the effects.
This time dilation effect has been shown to occur in real life, using hyper-accurate atomic clocks and supersonic aircraft. The clock left on the plane showed a tiny amount less time had passed than the clock left on the ground.
The idea that passing lightspeed might allow time travel comes from knowing that the instant before you reach lightspeed, the rate at which time passes on your spaceship falls to 0.00*absurd number of zeros*0001 seconds on your ship to every second on the Earth. At lightspeed, the rate would, in theory, fall to 0 seconds per second, effectively stopping time onboard. Technically speaking, we are time machines ourselves, since we can move, and thus alter the rate at which we travel through time.
Anyway, the reasoning goes: If the rate of change in time can be reduced by going faster, then surely it can be made negative by going faster beyond the point at which the rate is zero. If my account was working, I'd put in a graph explaining what I mean, but it's not, so I can't.
As for the G-forces killing you, that would only be a problem while you were accelerating, and you could mitigate that by accelerating slower.
G force is the force generated by Newton's Second Law. According to the law, the Force Acting on a body is equal to the mass of the body, multiplied by the rate at which it is accelerating (F=MA)
If you are not accelerating (ie A=0) then it doesn't matter the mass of the body, there will be no force acting.
With regards to what happens when you travel faster than the speed of light, I'd settle for the warp drive effect or the Battlestar Galactica FTL effect, but I suspect what you'd see as you accelerate is the light ahead of you being blueshifted, and the light behind redshifted (Doppler's law) and as you passed lightspeed, the view behind would be black and the view ahead white. Right up to the point where you hit something because you can't see where you're going, and nobody can see you coming because you're traveling faster than the light you reflect...