a question or two for all the computer boffins out there,

1, my laptop has just died - motherboard could be goosed, spilt liquid on it. now the question is are motherboards interchangable? its a dell laptop.
2, if the above cant be done, can the hard drive from it be switched to another lap top?
3, how much would a motherboard cost?
4, are you able to test the motherboard, keyboard, battery and the like?

thanks