Two main hurdles:
(1) Making the cables work. If either the LCD end or the motherboard end of the data cable are different, you're probably screwed.
(2) Making OS X realize you have a higher-resolution display installed. Since Intel Macs don't use Open Firmware, I can't help you with that one.
Check out the link on my sig image for how we did it in a clamshell iBook, but again...that was with OF. Different story.