Try "acpi=noirq" as a kernel argument. Some AMD chipsets have problems letting the OS know what irq the 8250 timer is on, the nvidia one is definitely a problem, I have the same chipset in a couple of Dell Dimension e521 desktops :-(
My explaination wasn't totally accurate. The acpi=noirq disables the ACPI IRQ routing table lookup for IRQ redirects and reprogramming. Some AMD chipsets had a bug in the way this table was built that caused 2.6 kernels to fail in getting a hook into the table which caused all kinds of intermittent problems. By disabling this feature you run the possibility of IRQ conflicts that will need to use the IRQ management in the BIOS to resolve. Updating the BIOS of the system sometimes fixes the problem.
It just turns out that the system timer irq was my "symptom" that I experienced, but it is different for different systems/configurations.
Thanks Ross. This does indeed make some sense. Currently we're trying with another known-good SATA disk just to rule that out then we'll give this a shot as well.
Ray