I am running a 55 watt Ivy i5 on my M3-ATX which only powers 125 watts. Look for lower wattage chips and you should be OK. 65 or 75 watt might be better to give you a little more "headroom".
Haswell chips are supposed to be more power efficient so you could always go that route as well.
Unless you are playing games you also don't need an i7. An i3 or i5 should do just fine. My i3 shows near max on the performance marks. I have a quad core i3 in my carpc and it handles everything I throw at it. I can always upgrade if I find the need later but depending on your motherboard you should be fine.
For instance here are some examples of some haswell chips:
i5 quad core 2.9ghz 65watt
i7 3.1ghz quad core 65 watt
pentium 3.2 54watt dual core