Just a newby asking the 64k question again - Arduino Mega2560

I don't believe this 256K FLASH memory can be used to store and retrieve data and is meant to be used for executable code only.

EDIT:

An near Arduino compatible such as the chipKIT MAX 32 may be more useful for your application.

Microchip® PIC32MX795F512 processor
80 Mhz 32-bit MIPS
512K Flash, 128K RAM

http://www.digilentinc.com/Products/Detail.cfm?NavPath=2,892,894&Prod=CHIPKIT-MAX32