Unfortunatley, aircooling peltiers on high wattage chips is a no go. You may get away with watercooling the peltier with heat-exchange in the process, or just using plain water-cooling.
Aircooling peltiers (like the Swiftech MC-371 does) is a good thing on like P3 700's, but durons take more wattage to cool, which then in turn takes more cooling in order to get the peltier effect working.
No. Your CPU will require a larger pelt and water to cool it. The rule of thumb is the pelt should be at least twice the size as the heat ouput of the CPU. For a hot climate a Swiftech or water cooling are your best options. Bong coolers in particular work well in the heat. It was 106F outside yesterday and 85 inside. Thanks to the bong cooler, my 1.6 gig Bird idled at 32C and peaked at 44C.
Funny you mention ducted cooling. I was just talking about this with a friend. John Carcich the retired engineer and thermal measurement genius cools his cpu this way, as does our own John "Hoot" Hill. Sounds like a plan to me!