On my old Dell Inspiron 530 (late 2007 model), the Ubuntu 12.04 ISO will not boot at all. It hangs at the splash screen while it's scanning for devices (I know this because I booted it after the first hang without the quiet splash parameters). It currently has Ubuntu 11.10 on it, running fine, but I prefer clean installs.
I seen one post where the user had a similar problem. He corrected the problem by entering the bios setup and changing the HDD channel/port from IDE to RAID. This corrected his problem. I run Vista 32 bit and Ubuntu 12.04 x86_64 on my Inspiron 530.
I had no problems installing, however, my system is a dual boot.