you could use an aircooled peltier, but you need to tell us what kind of processor you're planning on cooling with that.
if you are planning on using an air cooled peltier on your P3, then it's quite possible and practical to do. but if you are going to try and cool a hotter processor, then I'd have to say go with watercooled peltiers if you really want peltier cooling.
also, you'll need a cold plate. you sandwich the peltier between the cold plate and HSF, and the coldplate is what touches the CPU. good mounting pressure will be good for your temperatures.
besides that, you'll need to get yourself some good insulation, depending on your temperatures. otherwise you'll have problems with condensation.
have a look around the peltier section of overclockers.com.