A laptop are the same thing, just a portable computer. A netbook is inexpensive, small and usually not very powerful. Netbooks are mainly suited to casual use such as browsing the web and email hence "net" book.
Display size
Like i told you before, since laptops are smaller, they do come with smaller screens and resolutions. That is of course translated in a smaller workspace. Nowadays mainstream 10″ netbooks come with 1024 x 600 px res, and the next to come 11.6″ ones will have 1366 x 768 px .
8.9" netbook vs 15.4" laptop
The 15.4 laptops on the other side come with 1280 x 800 px (have a bigger dpi rapport, so everything is bigger on them and easier to read) or even 1650 x 1050 px. Bigger laptops can even come with Full HD resolutions.
Battery life
Netbooks are meant to be portable, thus a decent battery life is a must. Most offer at least around 5 hours of real autonomy, while the best can go up to 8-9 hours from a 6 Cell battery.
Few laptops can offer the same things. Of course, there are some, like the new ultra-portable Vaios on the new Macbooks, but they cost many times more than a netbook.
Price tags
Standard netbooks run for $200 to $450 , according to size and features. A good 10″ like the Asus 1005HA for example, with decent hardware and 10.5 hours battery life will only cost you around $360, while being light, durable and good looking.
Laptops on the other side can go for a lot more. It’s true some producers try to offer 15.4″ laptops for around $350 these days, but, you will get crappy hardware and crappy build quality, all in a heavy and bulky device. And that’s just not worth it.
Performance level
Here’s where the line is really drawn. Netbooks’ performances are limited by the hardware inside: they used low voltage CPUs that can only offer so much. They are good for everyday activities and even watching HD ready movies (720p, not 1080p), but not for games and other resources hungry applications. Performances level will increase in the future, with devices housing the Nvidia Ion platform (better graphic performances) and the new Intel CPU line, Pine Trail . But laptops will always be more powerful. Some a lot more powerful actually.