FFT analizer with grafic lcd

Hi. I am realy interested in building FFT Alalizer from www site
http://www.apetech.de/article.php?artId=7&nnId=17
I found some problems.
1. why the resonator frequency for Atmega32 is 18,432 MHz which only
calculate the FFT and put the data to TWI. Couldn't it be 16MHz.
2. What is the frequency resonator for the second module built on
Atmega128. It shows the bars on Lcd. Can it be 16MHz.

I am writing about this because I am worry about my procesors and its
stability, and i also don't have this resonator 18,432

Plesase reply for it, and please write in english because I don't
speak in Germany.
Slawek