You just take out the current deck, and din mount the new one on the left side of where the original one was. You will need a trim piece the put in there so that the 1 inch gap on the right isnt a big hole :P
Such kits can be found at any installer's shop, just get one to sell you one of theirs, or you can buy them online. I know Scosche (sp?) and Manta (i think?) make them.
If you want the deck centered, you will have to cut a small piece of plastic down there and get a custom trim piece. I highly suggest you take the car to a proffessional audio shop for this kind of installation.
Oh, note that, if you replace the factory unit, you lose steering wheel controls for the radio
There is an aftermarket product that can fix this problem, called the Pac Audio SWI-X; which depending on where you mount the IR eye, may not work half the time.