There seems to be some controversy about how many volts this thing needs. I've seen either 1.25V or 1.45V for the XP-M 2500+. I'm inclined to believe the 1.45V since that's what the other mobile XP's run at.
So far, the ONLY micro-atx board I can find that has undervolt options in the BIOS is this one:
Biostar M7NCG 400
It will 'undervolt' to 1.3V from everything I've read about it.
I've ordered this board myself (along with an XP-M 2500+) and hope to have everything in a week or so. Still need to find a mATX case I like though.
Will post feedback after I get everything up and running.