Well I guess it won't be a problem, because I'm running an Intel P4 2.6 HT (Northwood) with 2 gigs of ram, many usb's, 160gb hdd and 7'' monitor with M2 Atx which is 160 watts. In power consumption many Core2 Duo s are far better then a 2.6 northwood so the only problem of yours will be the GPU. But I think that GPU won't be that much problem because of the usage... Since you won't be playing Farcry in the car I think it won't be a problem even with the M2-ATX. So I think that with M4 atx it will be ok.
But I have a question about this mainboard. Does nvidia 7100 have 800x480 resolution support? If it does I'm also planning to buy one of these.