Upgrading stock power and ground wires...
 

I've got my new sound system installed and have been reading its a good idea to upgrade the stock power wires. I'm only pulling 800 wats RMS, but I am running 2 amplifiers at about 50 amps of current each. Would this require upgrading the oem power and ground wires?? Anyone have to do this yet?

the power you're going to run straight from your battery anyways. so no need to upgrade that

the ground you have some options.. you can run it to the battery as well (like I did) or you can ground it in the trunk and leave stock alone (which works ok) or you can ground it in the trunk and redo the grounds in the car - basically running 4AWG or better wire from the ground on your battery to the chassis and starter motor etc.... which will help all the electronics in your car.. and i've heard even smooths out the idle a bit..

You will want a run of 4 gauge wire from the battery, through the firewall with the main wiring harness (Careful punching a hole in that grommet).

As wikked said, you will also want upgraded grounding wires under the hood. They should also be 4 gauge, but you do not need a dedicated ground cable to the back of the car IMO. I grounded my system to the spare tire mount and use the chassis as a return. I just fired up my system today for the first time and I don't hear any noise, so I would say it's a decent grounding point (my multimeter agrees).

You can see the grounding point on the left of this image. It's the red wire with the yellow end cap. I had to file down part of the washer there to make it fit.
http://isomerica.net/~fluffy/Ren/powered-up.jpg