what is the difference between a netbook and a tablet.?

It's nothing to do with the operating system - you get Android powered netbooks and Windows XP powered tablets for example.

The definitive difference is that a netbook follows the basic laptop form factor: clamshell case with a keyboard and screen joined with a hinge. A tablet follows the flat "slate" form factor - flat design with no hinge. Although there are exceptions (especially in the field of specialised ruggedised machines) a tablet will also lack a keyboard and use a touch screen.

Tablets are like giant ipods. The iPad is a tablet. They are horrible for typing anything as you do not have a physical keyboard. Netbooks are like small laptops. They are hard to type on if you are used to a full sized keyboard but at least you have the option of plugging one in.

A netbook runs Windows (unless you consider the MacBook Air a netbook; it's more of an ultrabook), whereas a tablet runs either iOS (iPad), Android, webOS (HP TouchPad), or some other operating system. A netbook is just a small laptop, whereas a tablet is like a large smartphone. A netbook runs computer programs, and a tablet runs smartphone apps.

The netbook has an actual keyboard, while the tablet is just a touch screen.

the main difference is touch screen.