I have a 2002 and I put in some 6 1/2 pioneers over hte holidays. I bought some generic round 1 inch spacers from fry's for like $15. But the stock screw holes won't fit so you'll need to drill them on the door panel. They look like they are bulging out, but somehow they fit with room to spare. Unless the 2004 door panels were changed, you might not have any problems. Here are some pics following:

 

here's how the spacer looks on the door:

 

the factory plug is kind of custom, so I had to solder out the connector plug on the stock speakers. This required that I rip them out of the paper speakers. Then I solder on some generic connector wires at the contacts and that you can now hook up any aftermarket ones on with no hassel in the future.

Here's how it looks like when I'm about to connect them to the door on the driver's side.