I just put in a 6.5" component set in my 04. They went right into the factory location. However, I don't think the original wiring will work. The day before I swapped out my speakers, I had installed my Kenwood CD receiver that was hooked up to a sub amp and a 100w x2 amp for the front speakers. I ran the amp'* speaker wires to the wiring harness of the deck to power the factory speakers until I put the components in the next day. But, they wouldn't work. Fade to the front; nothing. So I had to run new wire to the doors.
Personally, I'd recommend running new wire anyway. The toughest part is snaking it through the rubber boot from the door to the car. Having the new wire makes hookup simple and really simplifies the process of replacing the factory equipment when it comes time to sell. That way, all the factory wires and harnesses are there.