Aaron Konstam:
I have had two problems from the first with FC6 on admittedly old Dell (circa 2000) hardware.
Ric Moore:
IRQ conflicts has to be it. I just installed FC5 to an older PIII and my ethernet card isn't found, although it worked fine with FC4
Can also be ACPI (seems to be full of bugs - ACPI, and its implementation, no idea about how good Linux software is to make use of it).
I've been going through this crap the last couple of days, trying out different versions of Fedora on the same hardware, each requiring different ACPI BIOS settings before it'd boot, find different bits of hardware, etc.