As chuck says a laptop and a notebook are usually the same thing.
But recently NETBOOKS have started coming out that are smaller (8" or so screens) and are smaller, lighter and meant for people on the move who want to stay connected to the interent.
Notebooks are generally smaller than laptops, about the size of an A4 piece of paper a notebook will have a smaller screen and will be slimmer, a laptop however can be very big indeed and hardly portable, some have 21" screen and just to confuse you further are known as desktop replacements.
Netbooks are generally smaller than notebooks are a relatively new thing, will have a lower spec and only really good for browsing and email on the move.
Be careful if you buy a netbook, I have an ACER one and it is a pain in the @rse. Certainly small to carry around, but for typing more thana dozen words....forget it.