Linux on usb hard drive or flash drive

I seen a thread in here that told people how to boot windows whatever from a usb hard drive. I was wondering if there was a way to boot linux from a usb hardd drive or a usb flashdrive.

how about a CD? see Knoppix (http://www.knoppix.net/)

I seen a thread in here that told people how to boot windows whatever from a usb hard drive. I was wondering if there was a way to boot linux from a usb hardd drive or a usb flashdrive.

Yes, there is. Some newer distros allow it without any hacks.

http://beginlinux.wordpress.com/2008/11/18/ubuntu-810-usb-drive-review/

Try the pendrivelinux site, they have lots of tutorials.

If the usb drive is at least 4 GB you could do a normal installation on it.