How to install Android 4.0 ICS in Virtualbox? Step by step installation guide

Finally day before yesterday I managed to install Android ICS with active ethernet and functional play store inside Virtualbox (which is inside Ubuntu 12.04). It took me 3-4 attempts with different ISOs. And to my rescue came the blog Android x86. I am heavily indebted to it, though I tweaked a few things here and there to make it work for me.

From Android 4.0 ICS

To begin, you need to