Motee in the spoiler forums has posted a good summary of the beginning to Episode III as best we know it. There are many sources for the report, including the normal rumor sites, the OS and some speculation. Here's a clip (in spoiler font) hit the link for the rest of part I!

INT. ENGINE ROOM, FEDERATION CRUISER - SPACE

The JEDI cross the floor of the engine room followed by more BATTLE DROIDS. Something hits the ship and liquid fuel begins to leak. The JEDI are unable to use their lightsabers. The quickly to try to escape the dangerous situation.

The pair of JEDI enter the fuel and make their way towards a VENTILATION shaft. Suddenly, OBI-WAN is attacked by a BATTLE DROID. The situation becomes more dangerous as the fuel makes its way towards some exposed ELECTRODES.

OBI-WAN manages to escape up the shaft.

INT. HALLWAY, FEDERATION CRUISER - SPACE

The two Jedi climb out of the shaft and into a hallway. ANAKIN seals the hatch behind them with his lightsaber. The fuel reaches the electrodes in the engine room and explodes.

EXT. SPACE

The explosion rips the FEDERATION CRUISER in half.

INT. BRIDGE, FEDERATION CRUISER - SPACE

OBI-WAN and ANAKIN fight together against GREVIOUS amongst raised platforms and sunken floor sections where there are duty stations. OBI-WAN climbs the illuminated stairs that lead to the expansive platforms to each side of the main floor.

OBI-WAN is hurled through the air by the GENERAL and hits the wall. He collapses. ANAKIN fights the GENERAL alone.

Outside the window, the ships begins to plunge towards the planet of CORUSCANT. GREVIOUS smashes through the window and escapes.

INT. EMERGENCY POD, FEDERATION CRUISER - SPACE

GREVIOUS enters an emergency pod and escapes.

INT. BRIDGE, FEDERATION CRUISER - SPACE

ANAKIN tries to take control of the ship as it plunges towards the busy metropolis below. OBI-WAN awakes.

Very cool stuff!