Ok.
So I have this 500GB external HDD I use as a backup for medias.
I know you can make a live disc that will be able to boot Linux off of on start up.
But in order to do that, do I have to format the external HDD?
Cause I don't have anything large enough to make a back-up.

And if I were to find something large enough, and install Linux, would I still be able to use it as I do with Windows, as a storage media, yet still allow Linux to be booted up with the boot menu?

It seems like I'd need to partition the drive into a boot drive and a storage drive, but I'm asking this so I don't accidentally wipe everything.

I have an older comp with Ubuntu on it, but the comp is too slow for it to be any fun to actually use, hence why I'm trying for it to be bootable from the HDD without damaging my current settings for Windows.

You would have to format part of it on which to install Linux.
First step, decide which distribution of Linux you want if you have already done so.
Download the iso image of the distribution.
Burn it as an image to a CD.
Boot your computer with the CD in the drive, have the CD drive set to first boot priority.
You should probably post more information on what you have, operating systems, number of drives/partitions for starters.
I'm not sure exactly what your intentions are? If you want to have Linux on the external and not have it attached at all times the procedure will be different. You could install the bootloader to the mbr of the external and then select it at boot time.
I'd suggest posting more specifics, the information asked for above would be a good start.

I'm wanting to install Ubuntu as a live CD to my external HDD.
I'm running an older Sony Viao running Windows SP3, but I have a different computer with Ubuntu on it.
I'd like to run Ubuntu from the Viao without modifying the internal HDD (which is partitioned into a C:\ and a D:\, both nearly full)

How I'd like to start Ubuntu is to mash F12 until the BIOS opens and I select the External HDD.
I'd like to keep it in a single partition, but it's not required.
But once it's installed, I'd like to still be able to use the same HDD for both Windows and Ubuntu the same way I use it now.

The HDD is attached most times, unless it's being used elsewhere, but the computer likely isn't on then.
But like I said, a LiveCD, so I can boot into Linux on other computers.

The external is unpartitioned.

I also found out a friend of mine has a 1TB SSD I can use to back up my external, so I can partition it.

bump

Bump...

You can install to usb, but you won't get the benefits of the os if you don't do the full install to usb. You'll have to have a boot loader atleast on the usb drive.

But if I were to partition the HDD, could I write the OS on one partition, and leave the other as a storage device?

Yes, I beleive so.
I'm not sure what boot loader will be good for you, but I'm sure that someone will lead you in the right direction.

Boot loader?
Meaning how? BIOS? Image writer?

Cause it seems I'd need to find a partitioner to make it work correctly...

Most Linux Os have it's own partition utility, you just tell it how much space it can have.
They also have guided partitioning. Just give it space and if you choose seperate /, usr, home let it make the default values for what you've given it.

Cool...

Why don't more people use Linux?

I'll be borrowing the SSD from friend tomorrow, I'll see how it goes.
I'll ask for help if needed.

One more thing, I have two computers.
One with Windows XP, another with Ubuntu.

Which should I install it on?

wait whatt????

didn't you say the ubuntu pc was slow?????

just stick the external drive into your pc, boot from a ubuntu live cd,in system,administration or i don't know which one you should be able to use gparted.

in the upper right corner of gparted select drive number 2
and make the NTFS partition it's got on it like 10-20GB smaller, and then use the buntu installer and slelect automatically use all continuous free space or something like that.
it will do the job for you.
you won't be able to access your ubuntu partition from windows (the 20GB partition) , but you will have access to the NTFS one from windows AND ubuntu/.
hope this helped some.

What you are looking for is duel boot System.I have done this on many occasions with Internal 500g HD running windows and added Linux in any form. I booted from install disk and told Linux to make its Partitions on 20g of main drive C leaving windows intact or send Linux to external drive if you want bearing in mind it will modify your boot sector on C to accommodate both programs.I would think all you should do is unplug external Drive while installing Linux (as I understand you to mean, it is only backup),The end result if you exercise due care at installation, the result will be at start up,you will be asked what system you want to start.The good news is you can access windows Files etc. from Linux The down side is that if you ever want to bring HD back to normal you have to clear master boot record and format HD To clear[fdisk/mbr] you will not see anything happen but mbr is gone.
Hope this helps as I am currently running two different systems on 2 internal HD but have to manually chose by my choice

Yes. It's on a Dell Dimension 3000. 'nuff said.

I'm trying to make a LiveCD (with the full, runable OS with data) onto a partition of my external HDD.
I'm using a friends external SSD to back up my HDD.
I don't want to do anything to my internal drives.
My goal is to be able to power the computer on, mash F12, open BIOS, and select the partition with Linux on it and boot from the external HDD.

But I say partition because I'd like to keep it as a media storage as well.
Unless I can do the boot alongside thing for a LiveCD without partitioning, I *think* I know what to do now.
We'll see.

See pendrivelinux.com for how-to's. There are basically three ways to run a live cd from an external drive.

One is to use the native fat format.

Another is to boot directly to a live cd ISO image.

Another is to make a native linux format.