How small of a Power Supply can i get away with?

Im messing around with my old computer parts tryin to make them into a htpc. the case i want to shove the parts in is very small so im very limited for space and all the small power supplys i can find are very low power.

The ideal (sized) powersupply im finding is a 200w. The parts I'm wanting to power is a old p5n-em hdmi motherboard with a Q6600, optical drive, Hdd, (optional: 1gb 9500gt graphics) and a wireless card. I plan on throwing XBMCbuntu on it. would 200 wats be enough?

Also the powersupply I found is made for mini itx boards but it says it will work with atx boards too. http://goo.gl/vepP8 . Currious thing is, it runs off a 12v power cable and the ones they recommend are for like Monitors and such and say they are like 12v 6amp 80w for example. If the powercable coming into the powersupply says it gives 80w, how is the powersupply going to give the system 200w?? makes no since. what do you think?

Nobody?

You're gonna need 400. Sorry bud. The 9500 is gonna need at least 350 to run from what I'm reading.

Well the graphics card is optional, I can deal with the integrated graphics.