Booting Ubuntu from an External USB hard drive

Hey.

 

I have a Dell Dimension 8400. I'm wanting to install Ubuntu on my desktop, but I really do not want to do a partition on my internal Hard drive. I bought a Hard drive that connects through the USB.

 

I know I can install Ubuntu to the hard drive, but what I don't know is whether my computer can actually boot from a Hard drive by accessing the BIOS (F2 or F3 - I forget xD)

 

Any help would be much appreciated.

 

Thanks