I decided it was time to place a PXE boot install image on my network for installing Ubuntu 10.04 Lucid desktops. For the most part everything went as expected (see this post) but during the install I got an error that "restricted/binary-amd64/Packages was corrupt".
It turns out there are no restricted packages on the alternate installer image, and the lack of an empty "Packages" file at "/dists/lucid/restricted/binary-amd64" where the networked install image is located was causing it to bomb.
touch Packagesin that shared directory within the install image seems to have fixed the issue. For some reason the fact that the Packages.gz ungzips into a zero byte file was throwing it, but having an already existing zero byte file seemed to fix it.