Hey i am trying to interface a 256mb external memory to my arduino board can anyone please tell me how to do it and the extra precautions that are to be taken

Part number?

is it RAM or EEPROM?

I2C or SPI interface?

something like this - http://ruggedcircuits.com/html/megaram.html - ?

my arduino board is LI2 arduino… don know much about what to use and all but my program code needs about 133mb hence for that i needed a external 256mb of memory storage

We need to know the part number for the memory device

What application are you making that needs so much memory yet (relative) so low clock speed ? Can you tell us a little more about that?

but my program code needs about 133mb

You can't use external memory to store program code. Only data. If your program needs that much space, you need to find another device to run it on.