This morning, found this blog post:
Herman Bos Â» Blog Archive Â» Got new hardware (DG965WH); yay; doesnâ€™t even boot
Normally Linux doesnâ€™t need to have its partition marked with the boot flag (windows does), so I didnâ€™t really guess something like this myself. But it seems that the Intel BIOS checks the partition table and only agrees to boot from a disk if a partition is marked with the boot flag.
Intel, you utter, utter cocks.