I'm not really a newbie, but not yet intermediate, so I didn't know where to put this question. But here goes.

I am trying to get my computer to boot into Linux. I have installed it onto my 250 GB Seagate external hard drive, and I am trying to get it to boot, but every time I try, it either can't find the root partition or it gives me error 17.

I think, in theory, I should be able to place the /boot files onto a FAT32 partition so I can easily edit the boot.ini file to get Linux to boot from the Windows bootloader (since I don't want to overwrite the Windows MBR, because I take this drive with me a lot), but I don't know if it will work, since most installers won't let me install the /boot files onto this partition (and I don't know how to do it manually).

What should I do?

Which distro are you using? The distro has to be specifically designed to boot off an external usb hard drive or that's exactly the error you will get.

Do you get the Grub error 17 before seeing a Grub menu, or before seeing the text "Press ESC to see menu", or do you get the error after selecting an OS in the Grub menu? In order to get a clearer picture of your setup related to your booting problem, how about downloading the Boot Info Script to your desktop (can be from a Live CD if you want), and then do the following as root user, but replace <username> with your username:
That will create a "RESULTS.txt" file in the same directory from where the script is run, namely your desktop; please copy/paste the contents of that file to your next post. That will help clarify your setup and hopefully what exactly is causing your Grub 17 error.

Your post is not clear at all. Do you have windows also on the external drive or are you referring to booting the external with linux from the internal drive with windows?? You seem to want to be able to boot from windows which shouldn't be that big a problem. It might be useful to provide this and partition information from fdisk -l if you don't want to use the script CJS suggests>

Alright, well I've tried installing two different ways. The first way, I left /boot under / and installed the loader onto the drive (instead of /dev/sda1, /dev/sda, if that makes sense). The second way, I put /boot into its own partition at the front of the disk. The first way, I got past the GRUB menu, but got hung up on the boot screen when it said that it couldn't find the root partition, and the second, I simply got an error 17.

I have not yet booted into Linux today, but I am going to within the next 20 minutes.

Which Linux distribution are you using?

Do you have another (windows) OS on the external drive?

Do you want to boot with Grub or windows bootloader?

/boot in root is a directory. For this to work, you need the stage1 file of Grub in the master boot record of the drive and it will point to the succeeding Grub files in that partition. This is simplest if you have only Linux on the drive but you haven't indicated if that is the case?

This would be the result of an incorrect entry in the /boot/grub/menu.lst file.

Cannot mount selected partition
This error is returned if the partition requested exists, but the filesystem type cannot be recognized by GRUB.

This error comes when Grub tries to mount a filesystem it doesn't recognize, windows. Grub does not boot windows, it chainloads.

If you can login as root with a Live CD and post the output of the "fdisk -l" command, it would be helpful. It's a lower case Letter L in the command, no quotes.