CPU generate heat in normal operation, the fans help cool it, but they shouln't be spinning hard all the time.

If you machine is making heaps of noise, when it isn't doing lots of processing (or using Flash) isn't good news thou, it could be malware or a virus.  Try running something like http://download.cnet.com/Spyware-Doctor/3000-8022_4-10293212.html to check.