It appears that a few of the dependencies for xserver-xorg-video-all have had their package file truncated in the 12.04 LTS 64 Bit Alternate ISO (ubuntu-12.04-alternate-amd64.iso). This causes Ubuntu setup to fail during the "Select and install software" phase giving an error message that xserver-xorg-video-ati and xserver-xorg-video-nouveau could not be installed.
Here are the package names from ubuntu-12.04-alternate-amd64.iso
\pool\main\x\xserver-xorg-video-ati\xserver-xorg-video-ati_6.14.99~git20111219.aacbd629-0ubuntu2_.deb
\pool\main\x\xserver-xorg-video-ati\xserver-xorg-video-radeon_6.14.99~git20111219.aacbd629-0ubunt.deb
\pool\main\x\xserver-xorg-video-nouveau\xserver-xorg-video-nouveau_0.0.16+git20111201+b5534a1-1build2.deb
I confirmed the proper package file names on us.archive.ubuntu.com:
\pool\main\x\xserver-xorg-video-ati\xserver-xorg-video-ati_6.14.99~git20111219.aacbd629-0ubuntu2_amd64.deb
\pool\main\x\xserver-xorg-video-ati\xserver-xorg-video-radeon_6.14.99~git20111219.aacbd629-0ubuntu2_amd64.deb
\pool\main\x\xserver-xorg-video-nouveau\xserver-xorg-video-nouveau_0.0.16+git20111201+b5534a1-1build2_amd64.deb
I can confirm that replacing the above mentioned packages with the ones from us.archive.ubuntu.com does solve the installation failure, and I haven't come across any other issues with the alternate installation media as of yet.
Fixed package name