I was in your shoes about a month ago. I know you wanted Via, but any chance you have a distributor who can get you a Aopen Pandora. The benifits of this machine are many. You get a pentium M board and a DVD/CDR-W drive in the package for $279 USD. It is smaller then Mini ITX and has more computing potential. The CPU's are cheap on ebay as well.
I looked into going the via SP13000 route and this just was a cheaper alternative all around since I did not need to buy a case or optical drive.
The only downside so far is that the stock resolution is 800X600 and not 800x480. However there is a thread that shows some hope on how to set up a custom resolution in the graphics driver. I have not tried it since I just got all my hardware and will be installing the OS tomorrow.
Also, one downside for you will be that you may have to sell the M2 power supply you have and purchase a Carnetix P1900 instead.