There are a few things that you need to determine.
When getting the two hours, are you doing anything that might be intensive that will decrease battery life (i.e. Flash content)? If you are, it is fully understandable that you're only getting two hours of battery life. (Remember that the Late/mid-2008 models with the removable battery have a theoritical max battery life of 5 hours but real-world usage is around 4 hours or less depending on what you're doing.)
If you're not doing anything intensive, try to calibrate your battery if you haven't done soon recently (142 charge cycles is getting up there).