I know this is an old Post, but I had the same issue with the HP 6305’s and their unfriendlyness with fog.
After wasting a week on research and different kernels, rolling back bios etc, here is what I found to work:
Ubuntu 12.04 with fog .32, running kernel 3.8.8
had to reformat the hdd with a NON hp Windows 7 disk and once the computer came up, I rebooted from the non HP Disk and followed these instructions:
I did that for the initial image, or golden image as some call it, and after that every computer has imaged perfectly, and very quickly.
Hope that helps!