Let me first back up to when I asked how I would find out whether /etc was on hdb7 or not. Out of all the directories, only /boot and /home are explicitly alloted their own ext2 space on the hard drive. I would assume, then that /etc is on hdb7.

While poking around, I discovered that my /proc/mounts file read as follows:

/dev/root / ext2 rw 0 0
/proc /proc proc rw 0 0
/dev/hdb1 /boot ext2 rw 0 0
/dev/hdb5 /home ext2 rw 0 0
none /dev/pts devpts rw 0 0
/dev/cdrom1 /mnt/cdrom1 iso9660 ro,nosuid,nodev 0 0

Now, I'll be the first to admit that I'm probably wrong (first of all, is this file re-generated with each bootup, or is it like a kind of xxxx.conf?), but it seems suspicious that there's no mention of hdb7. /root, yes. I also don't see my dvd rom listed here, though it's in /mnt as "cdrom". Further, I can put a linux cd in the dvd-rom, I can hear it spin up, the hard drive makes its thrashing noise, but I can't get any files to show up when I click on /mnt/cdrom. The reason I mention it is that this whole mess seems to have started about the time I installed the dvd-rom.

Thanks for your continued help.

Does anyone have any more ideas?

When I run dmesg, this line appears several times in series. It's the first place where something obviously looks wrong. Does this tell us anything useful?

hdb: dma_intr: status=0x51 { DriveReady SeekComplete Error }
hdb: dma_intr: error=0x40 { UncorrectableError }, LBAsect=8907344,
sector=3670088
end_request: I/O error, dev 03:47 (hdb), sector 3670088
EXT2-fs error (device ide0(3,71)): ext2_write_inode: unable to read inode
block - inode=229409, block=458761

I think it's safe to say that your hard Drive has bad sectors. If this is the first time it's happened to you, then congratulations, and welcome to computers... Back up whatever data you can still read. Reformat the haddrive with Error checking, (Or just run badblocks, I forget the options, but you'll have to do this from a book disk on an unmounted partition.) Assuming you find any errors this way, bring your PC to service shop for repair.

I very recently posted about e2fsck and badblocks in the Linux Newbie section.

It does sound like you have a bad sector problem (thrashing noises).

I recommend booting from a boot disk like tomsrtbt (a minimalist Linux distro). This way your partitions aren't mounted. In fact, use any boot disk that doesn't mount your partitions, and comes with the badblocks and fsck packages. (I think booting from RH CD-ROM and typing linux rescue actually mounts your partitions, so don't use it to boot from)

Once at the shell, type "fdisk -l /dev/hdb" (or /dev/hda whatever is your hard drive with linux) to find out your partitions. The extended partitions you won't have to worry about. You should see your /dev/hdb1, /dev/hdb5 and hopefully your /dev/hdb7 partition.

For any partitions that fdisk shows type being ext2, run this command on it (while booted from boot disk):
e2fsck -ccvf

this'll force badblocks to test every sector on the partition in non-destructive read-write mode. It might show you how many bad blocks you have. (I had 2 bad blocks on one of my ext2 partitions, when i had Windows on it, the drive made thrashing noises too)

Also, you may check out the integrity of your swap partition by running "badblocks -nvs" on it, while booted from boot disk.

I find this line interesting:

/dev/root / ext2 rw 0 0

I wonder if the /dev/root is a symbolic link to /dev/hdb7? Try running
ls -l /dev/root and see if it is a link to /dev/hdb7.

The thrashing has ceased!!!
Thanks to everyone for your help, and especially to Silly22 for your level of detail. I downloaded tomsrtbt, followed the instructions and booted from it. What a neat distro that is! I ran e2fsck manually (badblock option on--took hours!) on /dev/hdb7, then again (without badblocks) to get a 0 in response to the echo $?.

I still get some of the same error messages at boot-up (apparently mtab is in a bad block--think that might have something to do with it???), but the thrashing has gone and that's a biiiiiig step. Irks me about bad sectors, though; the HDD hasn't been in use for even a whole year.

Now, does anyone have any ideas on how to restore mtab to health?

Again, thanks. I seem to learn more about linux from doing this kind of stuff than anything else.