The only way you'd have any hope in Hell of it "just working" would be if the bigger display (it would have to be a bigger display, most likely off a 17" iMac I'm assuming, as just about any 15" LCD you'll find, including the one on the 15" iMac, will top out at 1024x768) were to come off the exact same model iMac as the one you have. The LCD in there is a bare LCD, with no controller or anything, all that is built into the motherboard, and LCD panels are extremely specific about which controller they need, you can't just mix and match willy-nilly.