Only your:
1. power unit needs fan
2. centre processor unit needs fan
3. graphic processor unit needs fan
For lappy, only your power unit need fan.
As for the technology now, we are using low heat centrino
processor.
For your power unit fan, you will have to go your lappy dealer to
change, coz it is integrated too... they will have to desolder the
unit, attach a new one and solder back.
Which means, normal people can do such stuff.. 
