How Can I Write Win 7 Paint?

All you need is

1. WPF project
2. Canvas control
3. (Optional) some common sense to add logic

Here is a sample project article[^] which is used to create simple paint-like application using WPF framework and Canvas control. You can Google for such other stunning tools and projects.

On Windows Forms, you can use Graphics object and draw objects on application's user interface. Another good thread for the same subject is this[^].

To make it look like Windows 7 Paint application, you are required to add controls and other styles that would make your application look like the previous one.