Still on my quest to build an ultra quiet, lower power consuming server using a Pentium M chip, I have found this socket 478-to-479 converter from ASUS. It allows a standard ASUS motherboard to run a Pentium M chip.
This has three big advantages over the Aopen board(s) :
1) I can choose a board most suited to my requirements (SATA RAID etc)
2) The CT-479 can support either 533mhz or 400mhz FSB processors, given that I'll probably be buying my processor through eBay this will allow me to be a bit more flexible.
3) Much cheaper ! From what I have seen, the Aopen Pentium M boards are twice the price of most motherboards.