This is greatly unlikely, it's a brand new Dell XPS not even a year old. It seems that it's a hardware issue (SATA disks) but the fact that it appeared only when FC5 was installed on it points somewhere else. On the FC4 side the lockups appeared only when newer kernels were installed. Back in December the machine was running for 3 months uninterrupted doing heavy calculations with absolutely no problem.
I'll turn off APIC and see, but this cannot be a permanent solution since the machine is dual core...