I have installed Ubuntu 8.04 on the second partition of an external usb drive and I already had Win XP installed on my internal drive. With the external drive connected and booting from my internal disk I can get the dual boot menu and both OS's boot fine. With both drive still connected I try to boot Ubuntu from my external disk and get an error saying that it cannot find the partition.

My goal is to be able to boot XP as I always have when my external drive is not connected and have the dual boot option when my external drive is connected. I know that when I installed Ubuntu I placed some of the boot files in the wrong place, this is what I am trying to repair, and I am trying to do it without having to reinstall linux. I also know that in order to boot XP without the external drive I will have to repair my MBR with the xp repair prompt, I am ok with this and I believe that I know how to do it. What I am really hoping that someone here can help me reconfigure the GRUB on my usb disk so that I can boot Ubuntu.

Thank you in advance!

The best way to get it to work is to install Linux on your (large, fast) internal drive, then boot from Windows on your (slow) USB drive

PS:
I assume your BIOS supports booting from an external USB disk, and I presume you've configured the BIOS to do so

http://www.novell.com/communities/no...hout-dual-boot

To do what you indicated you wanted in the second paragraph of your post, you should have installed the Ubuntu Grub stage1 to the master boot record of the external drive. You could then easily put an entry to boot windows in the menu.lst file.

In order for anyone to give you specific advice, you will need to post the output of the fdisk -l command, your partition information. If you have your install CD or any Linux Live CD, open a terminal login as root or use sudo fdisk -l (lower case letter L).

I would fix my xp boot loader back to MS. Then I'd change boot order to boot to the usb external when I wanted linux.

I guess you could set the default for grub on the internal to xp and only boot to linux if you select the second choice.