Low power consumption linux pc project

I've managed to get my hands on a mini itx board, a cdrom and a power
supply to go along with it. I would like to use it to build a low
power consumption server for serving web pages. I have a few
questions about how I should go about this. I have been toying with
the idea of using a USB key or something similar as the primary hard
drive, or as a swap drive to a hard drive that would be idle most of
the time. Is this possible/a good idea? If I do get a hard drive for
it, what would be my best bet for a low power consumption hard drive?
I was thinking a laptop drive would be ideal - it doesn't have to be
that fast or large.

Anyway, I was wondering what thoughts were on this, I'd be really
interested to hear if anyone else has attempted something like this.