Other ATmega/AVR
To use a different ATmega/AVR chip, you'll need to make changes to the Arduino core, which is in the hardware/cores/arduino sub-folder of the Arduino application directory. This shouldn't be too hard, but it will require reading the datasheet for your chip. In particular, the names of registers and register bits are likely to vary between microcontrollers.
Which Files i need to Modify in the hardware/core/arduino to accommodate different ATMEL AVR's and what would be the modification?