I installed an AVIC D3 in my '07 Subaru WRX a couple weeks ago but have not been able to get the nav to work correctly so far. The arrow showing direction of the car is always drifting to different directions than what the car is traveling in. Sometimes it will be pointing in the right direction, then drift off to the right of where I am traveling. The last day or so it has been pointing directly to the right. I've read through the manual but can't figure out how to correct it. Right now I have the nav antenna in the corner of the windshield on the passanger side. Is the placement effecting the nav?

Placement could very well be your issue. Some people say that it takes a few weeks for the device to learn your area. I say thats BS. Try relocating the antenna and see if you get better or worse results.