Notebook and laptop have largely become words for the same thing, so there isn't much of a difference. Once upon a time people used Notebook to mean a computer that was in a smaller, more portable class , while Laptops tended to be bigger and a little clunkier. Now there are so many options for size and weight, the distinction between the two isn't very clear.

On a side note, NETbooks tend to be smaller and more portable than traditional laptops (or notebooks). They are designed primarily for surfing the web on the go and with portability in mind, so they tend to have more modest hardware and many don't have an optical (CD/DVD/Blu-ray) drive.