Rich text box

Is there any open source Rich Text box control like the control where I am writing.

Actually I have to take input in Richtext box and write it to htm file.

Check the open source FCKeditor - http://www.fckeditor.net/

I want control, for ASP.net 2.0 open source. it is for php. how can i use this in my asp.net 2.0 web page?

Check this article for detailed instructions on FCKeditor - ASP.NET Integration:
http://docs.fckeditor.net/FCKeditor_2.x/Developers_Guide/Integration/ASP.NET

Also check the Rich Text Editor ASP.NET Control, RTE at Codeplex - http://www.codeplex.com/rte