So by the looks of the mini-ITX systems on this site, I should be able
to build something that looks good, and runs directly off of 12v using
the "Cubid silent 12V DC-DC Converter Kit " (
http://www.big008.com/ProPage.asp?ProID=PI160300 ) - correct?

One that I know of is at http://www.big008.com/catPage.asp?catid=CI01250000
. However it is only 55watt, designed for the low power end of the mini-ATX
form factor. If you find one suitable for ATX, let us know!