OK, /dev/sda1 is mounted on "/media/DED8216ED82145DD". You can take a quick look at it and verify that it's OK, but I can't think of any reason it wouldn't be, since it mounted.

Looking at your df -h, I see that "/" is mounted on /dev/sdb5. That still indicates to me that you have changed the BIOS so that SDB is the boot drive. I'd check the BIOS and see if you can set it back to SDA, which I take to be your internal drive. With any luck, it'll boot, unless I've skipped over something when reading your post. Otherwise, you'll have to follow syg00's and yancek's advice to boot from a recovery disk and run fixmbr or fixboot.

Added:
Still, I'm surprised it won't boot from grub, unless you've really made a hash of the XP drive.

will it matter if the Startup CD i use is for a different edition of XP than is on the hard drive?

how do you do this?

It shouldn't matter which version of XP you use for the fixmbr program.

Generally, you can get into the BIOS by holding down the delete key when you first power it on. Generally the arrow keys move you around in the menus. On the systems I've seen, the second menu structure contains the boot order. Just to verify, what happens when you try to boot without the external drive attached? If you get grub errors, then yes you will need to run the fixmbr program.

yeah i get grub errors. i'll run fxmbr and see what happens

i can't find an xp boot disc anywhere, any idea where i can download one? well, actually that's not true. i got one and i can use it to boot windows, but i can't enter recovery mode from it. (i used it in another computer that said the file hal.dll was missing or corrupt on the disc)
i think it's also useful to mention that Windows recognizes my C: drive (the external one) as a USB drive, and my windows-compatible partition of my USB drive (E: ) as the Local Drive