Fox

Biggest issue I've seen is that there's been no standardization for the peripheral drives of laptops. For the most part, one laptop hard drive should work with any laptop. Unfortunately, as you probably already know, this doesn't apply to the CD-Rom drive, floppy drive, or battery. You'd also probably have problems with setting the screen up correctly as I think most brands have their own way of doing things.

Assuming you could find parts that work with each other, the hard part would be getting them to fit in one tiny case. This is where the car to automobile comparison really comes into play: older cars, for example those old huge fords and chevys, could handle a reasonably bold engine swap, because the innards were simple enough that they could jive with a little work. Like new cars (especally japanese imports), laptops are made with compactness in mind, and every one has its own layout and method of assembly. When my one laptop broke, I couldn't even open the stupid thing the whole way because it was put together in such a complicated way. There are disassembly guides, but unless you can find them you're pretty much out of luck if you have one like I had.

That said, if you're going about this just as a learning experience, go for it. I think it would be fun to make a totally impractical laptop out of a metal "pizza box" and run it off a motorcycle battery. But if this is to save money, you probably won't succeed. But it's clear from your post that you have the experience if you do plan on trying it.