I haven't tried it, I've never opened a laptop for anything but a RAM upgrade, and I have no clue where to get parts... but yes, I've heard it's possible.
Now, its more than likely not worth the effort, as it involves things like variable cooling and dealing with highly sensitive components in tight quarters. Older laptops (and maybe newer ones too) are more-or-less "packed"... open one up and the thing basically pops.
Hit up Google for more info, I'm sure you'll find something.