What kind of music do you listen to? What are you trying to accomplish?
Unless you have some form of measurement mic and frequency analysis tools, you can only tune it to what you think sounds good. Start by playing a long CD of music you typically listen to. Get the balance front to back correct first, then the balance between the left and right. Then start with each frequncy band at 0. Adjust an individual band until you think its perfect. Wait a few minutes and listen. Let your ears adjust to the change you made. Then move on to the next band. Adjust, wait, repeat till your done. You are now close to perfect. Save these settings. Then drive around. You'll probably find you have to make minor adjustments to account for road noise. I'd probably take the average setting between the levels you set while the car wasn't moving and the levels you set while the car was moving to give you the best overall sound at any driving condition.
If you want to be real fancy, you can set multiple EQ curves and have then crossfade between each other as a function of your speed. Increasing speed = increasing road noise, but that noise isn't all equal in every frequency band. Its much more prominent on the low end. Since you have a carputer, this is possible. In fact, since you have a carputer, I don't understand why you have the EQ since that can all be done through software. But that's another thread.
