most motherboards come with software that will monitor CPU temps. Its worth keeping an eye on this especially if they are using AMD chips as these get HOT!

re your question about how to connect up a PSU. The psu should come with all the connections you need. All you simply do is unplug the exisitng power supply loom in the same way you would a cars loom, remove the power supply and then replace with the new one and reconnect everything back up with the new loom from the new power supply.