Code:
wget http://files2.zimbra.com/downloads/6.0.6_GA/zcs-6.0.6_GA_2324.UBUNTU8_64.20100406201708.tgz
tar -xzvvf 6.0.6_GA/zcs-6.0.6_GA_2324.UBUNTU8_64.20100406201708.tgz
cd zcs-6.0.6_GA_2324.UBUNTU8_64.20100406201708
./install.sh
Then answer the questions accordingly
Ofcourse replace the download link with the one appropriate for you OS.