I'm trying to install Ubuntu 12.04 on a Macbook Air 1,1. I made a live USB stick using Penguintosh (the more common methods failed). Now, the regular amd64+mac installation hangs the moment I click on the installer, with an endlessly spinning cursor and nothing else, although the live desktop works fine before that. I tried suspending the computer to unfreeze the hard disk, as recommended in one place, but that doesn't solve the probblem

The alternate install gives me a grub prompt and nothing else. Typing "boot" at the command line gives the response "error: no loaded kernel".

Can anyone help with either the regular or the alternate install?