Can you change a CPU in a laptop?

[Warpy]

Hello,

I'm going to be getting a second hand Dell D630 off a friend and It only has a 1.6GHz processor. Would I be able to purchase a 2.4GHz Core 2 Duo and install it?

I'm not familiar with laptops so forgive me!

 

[Warpy]

are they expensive as opposed to normal desktop CPU's?