This process will take an hour or so, but it will fix the leak.

The problem is the drain in the cowl in front of the windshield (which is also the air intake for the AC system) is clogged. When the drain clogs it runs in through the fresh air vent, through the blower motor, and onto the floor.

You need to remove the plastic parts that cover the air intake. It will help to raise the hood to the verticle position. There are screws, plastic clips, and as I recall, little plastic buttons that hold those pieces in. You need to remove the whole thing, as the drains on the driver's side are probably clogged too.

This is the piece that you are removing:
http://tad.grosvenor.org/gallery/C280Mods/IMG_3051

The most important drain is right behind the right front wheel, in the engine compartment. This tends to collect leaf litter that sifts its way through the plastic cover on the intake. I used my finger, the hose, and a bent coat hanger (to get to the vents under the wiper motor) to clean the drains on mine. Once you get the cover off, you'll see the air intake, and the drain.

This is the bottom of the air intake box. You can see the pine needles in the drain on this one. Be sure to clean the debris from the area outside of the drain too. On mine it all flushed out onto the ground without too much effort.
http://tad.grosvenor.org/gallery/C280Mods/IMG_3053

-Tad