Can I install on USB HDD?

I see its possible to install and run DSL from a USB drive but can this be done with Ubuntu too?
Looking at installing all of linux direct onto an external USB hard drive and running entirly from that drive.
I can boot from USB with no problems but currently running Vista Bus. which I use for work. All the work crap takes up 80% or more of my hard drive so I want to ustilise my USB 2.0 20GB hard dive to run Ubuntu. I don't really want to work about bootloaders, new partitions. Ideally Just want to run from USB, possibly moving between two machines if possible?

BTW new to linux so please be patient with me. Only used Ubuntu via VMWare Workstation so far