Q: How do I diagnose some errors that appear to be possibly hard drive or memory-related?

Some /var/log/messages of late indicate errors:

saccade kernel: EXT2-fs error (device 08:02):
ext2_free_blocks: Freeing blocks not in datazone -
block = 51346892, count = 1

followed by:
saccade kernel: Unable to handle kernel paging
request at virtual address c312bd68
saccade kernel: VFS: Wrong blocksize on device 8:02
saccade kernel: Kernel panic: Free list empty

On the most recent boot, we got this startling message:

saccade kernel: Uhhuh. NMI received.
Dazed and confused, but trying to continue

A: You probably have a hardware problem with your RAM chips or a power saving mode enabled.

The messages above point to hardware problems. They don't seem to point to any one area. I'll bet memory, but that's just following the odds. It could be mother board or CPU, however. I don't think it's your hard drive, judging by the above errors.