Just like this "Post New Thread" works..
How can I get all these formatting icons in my aspx textareas? Any Javascript or .Net plugin?
Microsoft should do such controls.. they are so much in vogue

This is a pretty tall order, actually. There's a lot involved in coding this type of text-editor. Generally it's called a WYSIWYG text area, and a number of companies offer them on a free or fee basis. The quality varies widely between them.

One that's apparently pretty popular is this:


I haven't used it yet, but I imagine you just drop it right into your project as a reference, and then use it as a custom control.

I guess it just has a .Text property like a regular TextBox, and you get back HTML code.