ok update on this.. I thought I would just go ahead and try it..
Sadly, the M1ATX device wont do what I wanted.. It will turn the laptop off, but wont turn it on ..
You have to short pins 14/15 together to make the m1 output on the 12v rail, but I dont think the signal to turn the laptop on it correct. On another down side the dc dell adapter that I've been using for about 6 months on mains (dual 12v and mains adapter) decided to pack up yeasterday. I thought I had fixed but, but a crimp in the wire seems to have damaged some circuit inside it.
so now where do I go.. hmmmm order a new psu for the dell £60 + vat + postage and build myself a relay circuit to turn the dell on.