hehe, this is the update of the story:-
NC4200 upgrade to NC4400 is not that easy.
1) Motherboard. the dimension, screw holes, LCD connector are exactly the same. Component wise, WLAN is completely different, u have to buy WLAN card for NC4400 separately. minor issue.
2) NC4400 is SATA, the connector will stuck at bottom case during installation, need some plier/cutting work to make way for it. small issue.
3) Power connector different between 2 models. Still able to install by removing some obstacles at the rear keyboard cover. small issue.
4) LCD screen. Although the LCD screen connector is exactly the same, after fixing up the system will not start. removing the cable it will start, so something is not compatible between LCD screen of NC4200 and NC4400. this is major issue, I have no solution yet other than replacing the LCD. This defeat the purpose of 'upgrade' because it is cheaper to just grab a used NC4400 laptop from the shop/online seller.
*** CPU of course not compatible between the 2 models. RAM wise, NC4200 is 533, NC4400 is 667.