The M2ATX is not the best solution for your EEE PC. The M2ATX is designed for a desktop-style motherboard that is ATX-compliant.
I suggest reading this FAQ: http://www.mp3car.com/vbulletin/advf...iew&advfaqid=6
It should help shed some light on different power supplies for vehicle use and what types of systems they are best suited for.
There are other FAQs about power supplies, as well: http://www.mp3car.com/vbulletin/advfaq.php
You want a regulator that puts out the same DC voltage as the power brick that you use to plug it into the wall at home.
Chances are there is a Carnetix model that will meet your needs quite nicely.