Up till now I've always run Ubuntu in a virtual machine. The reason I want to be able to boot from a USB drive, is so that I can use accelerated graphics in compiz, which required the ATI drivers that don't work in Vmware fusion or using the Ubuntu 7.10 LiveDVD.

I have an iMac Core Duo with OS X taking up the entire internal HD. I installed Gutsy on an external USB drive using the LiveDVD. In the installer selected the option to use the entire Disk. then I used gparted to check the partition table. I got the following partitions.
/dev/sdb1 ext3
/dev/sdb2 extended
/dev/sdb5 swap

while still in gparted,I set I set the boot flag on /dev/sdb1

When I rebooted holding the option key, my internal hard disk was the only disk that showed up in the bootloader.

One thought i had was to use a cd as a bootloader. If so where would I get such a cd (iMacs have EFI instead of BIOS, so the disk would have to be compatible) or what would be directions for creating it. (I'm not much of a techie, so it would hae to be spelled out the step by step in plain english)

If someone has a better Idea, I'm open to it as long as it's something thats not technically over my head. I really don't want to mess around with the partition table on my internal HD. sice the USB drive my Backup drive and for the moment I don't have a back up.

I am not really familiar with MACs nor with EFI, but it would seem rather strange to me, that it would automatically recognize that it can boot into the USB device. First, check if your MAC(the model) is able to boot to an USB, and then look up how. Just google it, or mess around with the EFI interface (I guess it should have one).

If it cannot boot directly to it then try with elilo It would actually mean to "mess" with your internal hard drive but if it works similar to grub you can probably only install it to the mbr and then have it point to the external usb drive for the next stage, but that would mean you would always have to have your external hard drive for booting into the internal one. It could even be that elilo installs completely on the mbr of the efi, but again I repeat, my knowdlege on EFI is vague.

About the CD, here is a list with resources for making your own live cd, which then should only be a cd that boots into a bootloader that can handle both OS' on the different drives or at least boot the one from the external drive. Sound somewhat strange to me and not really useful, but it is always nice to get your hands dirty doing such work.

I hope this post helps,I don't know that much on the subject. At any rate your best friend should always be google. Search it, the solution is out there, I'm sure.

Thank you for resonding, but most of what you said is technically way over my head, and the rest is uncelar because you are just guessing about macs. Ive spent toons of time lookingon google and in forums, and i haven't found anything that solves the problem for me, and most of it is written for hackers, not cheerleaders. Thats why I'm looking for a simple step by step solution written in plain english, or something ready made that I can just download and run.

Well, what type of Mac do you have 2cute4u? Any special configuration?

And why not boot from the hard drive? Is EFI stopping it or something, or are you really just using all available space? (From BootCamp you can shrink your partition and emulate the BIOS so ubuntu should be able to install)

Some motherboards just can't boot from USB.