Don't listen to wusy, you can't stack peliers like that! When peltiers are cascaded like that they need to be perfectly matched or else one will overheat. You can place them side-by-side though.
One important factor that escapes most people is that the peltier will only pull out its maximum rated power with no change in temp between the hot and cold side. So if a 75 watt peltier is given a 75 watt heat load the hot side and cold side will be the same temp. If you want to cool a 1.2Ghz Athlon effectively you need at least a 150 watt peliter.
Using peltiers correctly is complex. Here are some good links.
<A HREF="http://www.melcor.com/handbook.htm" target="_new">http://www.melcor.com/handbook.htm</A>
<A HREF="http://www.electronics-cooling.com/Resources/EC_Articles/SEP96/sep96_04.htm" target="_new">http://www.electronics-cooling.com/Resources/EC_Articles/SEP96/sep96_04.htm</A>
<A HREF="http://www.tellurex.com/resource/txfaq.htm" target="_new">http://www.tellurex.com/resource/txfaq.htm</A>
<A HREF="http://www.sirec-it.com/faq.htm" target="_new">http://www.sirec-it.com/faq.htm</A>
<A HREF="http://www.electracool.com/basics.htm" target="_new">http://www.electracool.com/basics.htm</A>