Most of the people here use the m10000 model.
You can find the specs here:
Here is a review of the board:
The m10000 board uses a VIA C3 processor running @ 1GHz.
This is a special CPU designed to consume as little power as possible and run as cool as possible. A pentium III CPU has more power but a C3 CPU is more suitable for special missions like a carputer project. They both are x86 compatible CPU's. Just to give you an idea the C3 consumes just 45Watts when it plays DIVX movies @ 90% CPU load while a pentium III could easily reach 65 - 70 Watts. The new generation of C3 processors (we will see them on the Nano-ITX boards) can run fanless @ 1GHz. So no direct comparison. You choose what suites you best.
You can buy VIA EPIA boards everywhere nowadays.
Check this site. They ship worldwide :
Hope this helps.