What do the different millimeter offset numbers mean? Is it possible to make the stock 03 SE rims move more outwards, so they don't sit "inside"
of the car so much? I am pretty sure that is what offset is, but I don't know the details..

 

Anyone know?

 

Wheel offset is the measurement in millimeters that the lug holes are from the center of the width of the wheeel.
Spacers are available to change the offset, try Apexi

 

You want to move your stock rims further out for some reason? Why? I wouldn't do this because you'll get more steering kickback and if you go too far you might get an interference problem....

 

Here is a quick explanation from the tirerack:


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The offset of a wheel is the distance from its hub mounting surface to the centerline of the wheel. The offset can be one of three types.

Zero Offset
The hub mounting surface is even with the centerline of the wheel.

Positive
The hub mounting surface is toward the front or wheel side of the wheel. Positive offset wheels are generally found on front wheel drive cars and newer rear drive cars.

Negative
The hub mounting surface is toward the back or brake side of the wheels centerline. "Deep dish" wheels are typically a negative offset.

If the offset of the wheel is not correct for the car, the handling can be adversely affected. When the width of the wheel changes, the offset also changes numerically. If the offset were to stay the same while you added width, the additional width would be split evenly between the inside and outside. For most cars, this won't work correctly. We have test fitted thousands of different vehicles for proper fitment. Our extensive database allows our sales staff to offer you the perfect fit for your vehicle.
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Here is a great calculator for determining what offset will work on your car:

http://toy4two.home.mindspring.com/offset.html