I just got back from Kokoda, so I'll add acouple of thoughts while they're fresh:
1. Dan's right – train, train and train. While it can be run in a day, those guys are incredibly fit. Most of us aren't. Do as many steep hills and stairs as often as you can. You'll be going up or down all day every day. The only flat parts of Kokoda are the Swamp and across the top of the range through the moss. Maybe a1km out of 96.

2. Consider hiring a porter. It'll make the trip a whole lot more enjoyable. Hiring a tent up there cuts down on the weight ex Oz as well.

3. Hydro pack / Camel pack for sure. We went through minimum 4L per day water and 1L Staminade. We didn't treat the water, despite a water filter and puritabs. The guides were confident of the creeks we got water from and we had no problem.

4. 3 socks was plenty – but they were top quality hiking socks. I saved the 3rd pair for the last day. What a treat. Make sure you take a cheap pair of sandals – not thongs, thongs would be a bastard walking through the creeks. PLenty of tinea powder of a night and we had no problems with our feet.

5. Forget the poncho / raincoat. I was happy with a pack cover to keep my gear dry and just got drenched when it POURED rain of an afternoon. I was already drenched from sweat so couldn't get any worse.

6. 2 sets of clothes is plenty. Wash out the day set of a night to cut down on the stink. Evet camp we stayed at had plenty of running water – either a creek or hose pipe. Some had showers. Your day set will start of wet but even if they started dry they'll be drenched with sweat within minutes. Why worry.

7. Take the cheapest, coolest sleeping bag you can get. Somwthing for $20-$30 will do the job. I used mine once and gave it to my porter.

Other than that, enjoy the track. It's hard at times but certainly can be done by anyone reasonably fit. Just remember, the fitter you are, the more you'll enjoy it.