my macbookpro is getting heated and very slow after i updated Software to Mac os x 10.6.8

Recently i updated my macbookpro software to mac os x 10.6.8, after update CPU fan is running non stop even when laptop is idle and laptop is getting more heat thn laptop is too slow,videos are playing very slowly.its very weird.

some one encountered same issue after update???is there a way to revert the software back to previous version??please help

my laptop configuration:-

Model Name: MacBook Pro

Model Identifier: MacBookPro7,1

Processor Name: Intel Core 2 Duo

Processor Speed: 2.4 GHz

Number Of Processors: 1

Total Number Of Cores: 2

L2 Cache: 3 MB

Memory: 4 GB

Bus Speed: 1.07 GHz

Boot ROM Version: MBP71.0039.B0B

SMC Version (system): 1.62f7