At the moment, the leak ICS is only available for the China model i9100g. Our i9100g need different bootloader in order to run this. So, we can't flash it through CWM or Odin. Otherwise your phone will brick if you try.
If you have china i9100g and you want to root on this ICS. Follow these step:
1. Download this CWM & ROOT.rar
and extract it. You will have two files.
2. Put the extracted file CWM.zip in external sd card and 1234.zip in internal sd card.
3. Turn off your phone. After that turn on your phone into recovery mode. (press hold menu button, Volume up and power button)
4. In the recovery mode, goto [apply update from external storage], choose the file CWM.ZIP and press yes to flash.
5. Now you should have temporary CWM Touch Recovery, now go to [install zip from sdcard] and choose the file 1234.zip to flash.
6. Reboot your phone and you have rooted your phone.