Ask YC: Coding War Games Definition Required

I am planning to have Coding War Games for developers in my company. It will run for 24 hours and teams of 4 developers each will take part into it.

The idea is taken from Peopleware as most of you must be knowing.

I have explained the terms and condition for the event here:

http://dev.digi-corp.com/2009/02/coding-war-games/

Now as per the book the definition should require efforts from 1 man month to 2 man month. And it would be good if it is taken from some project which company has already done.

We people work on PHP, ASP.NET and VB.NET mainly and thus would like to have definition which is platform independent and can be written in any of the 3 languages.

Have you people taken part in such type of Coding War Games? Can anyone suggests good definition for the event which is exciting for developers to code in 24 hours?