I was trying to install Ubuntu 12.04 on the lab machines and the installation process hangs after displaying the world map to select the time zone. This happens with both 32 and 64 bits versions.
I found a solution now. This problem occurs because when we are selecting the time zone, Ubuntu does need the Internet connection to get the information. If it cannot do it, the installation will hang.
So, I just need to restart and select 'Try Ubuntu' first to make sure I can really access the Internet. I can then successfully install it.
Hope this helps!