Addressing with Micro rontrollers

Hello,

How can we give an address to a chip like ISD by using a microcontroller like Atmega8 ?

I want to record voices at special addresses, and then play them back.

Which part are you talking about, there are a number there. Most seem to have an I2C or SPI interface. What you have to do is look at the programming commands, for whatever chip you are using, these should tell you how to put messages at a particular address, and how to re-access them. There should be a table, showing which control bits to set, and an address value.
Then it is just a matter of sending those commands via SPI or I2C from your Atmega8.
There are probably application notes that will help,
cheers,
Richard