I would have to agree that it is not worth upgrading the CPU in your laptop because the other issue is the integrated Intel GMA 4500M video chip is rather slow and cannot be upgraded.
If you have an AMD CPU in your laptop, then you have a Radeon HD 4200 chip in there which is not that great either, but better than Intel. It also cannot be upgraded.
Sorry to say, but you need to buy a new laptop if you want to play games and you probably need to consider a $600 - $700 budget.