Ok, put a Phenom and a compatible motherboard and a power supply in your toaster. Most people would consider this a case mod. Put a Core 2 Quad in an NES and you get the all too famous "NES PC" mod. For that matter, cram a motherboard into a dead beaver, I've seen it done online somewhere, it's a PC! The form factor of it is a laptop, yes, but inside are PDA parts hooked up to a bigger screen and a keyboard. It's not a "full" laptop in the way you'd consider a laptop, doesn't have x86 so you're really limited on OS. It's not completely a PDA either, since it's bigger with a keyboard. It's more in between, combining some PDA elements with laptop elements.
If it were in a tablet PC form factor then it would be an oversize PDA, but instead it's a laptop with PDA parts.