Learn Validation Controls of Asp.net

http://msdn.microsoft.com/en-us/library/aa479013.aspx

http://msdn.microsoft.com/en-us/library/aa479045.aspx

BEST HTML EDITORS

Choose best which sutes for your requirement

I like this http://www.webresourcesdepot.com/wysiwyg-editor-with-a-file-manager-elrte/

http://pietschsoft.com/demo/jHtmlArea/

http://remiya.com/htmlbox/index.php/11/demo/skins-demo.html

http://plugins.jquery.com/plugin-tags/wysiwyg

http://www.webresourcesdepot.com/category/goodies/wysiwyg-html-edit/