Be sure to read the comments that follow the tutorial. There are some
caveats that you will want to know about before you do this. For
example, this is an *installation* tailored to the machine that you did
the installation on. Taking the usb stick to a different machine may
not work.

Try http://www.pendrivelinux.com , have good tutorials to.

i'll be giving it a try. Running ubuntu from
usb is mentioned in Ubuntu Hacks by Oxer, Rankine, Childers. Just says
that it can be done but enough detail.