Even though Companies do masses to keep the proccessor cool but in the end, the no air-flow/tight space means it gets really hot. Many magazines have said that, with most laptops, after and hour or so you may smell a hint of roast thigh.
Overclocking a loptop is a bad idea, I wouldn't be surprised if the keyboard started to melt afterwards!
Overclocking a laptop is a sure fire way to destroy it.
Also, if your only using for work, it should be fine, but a PIII is an absolute no-no for gaming, like asking a baby to lift a young whale!
If you want to game, you'll need a new one, but laptops really lag compared to comparable price desktops.