Hi,
Please check out these links
C# code
http://aliraza.wordpress.com/2007/07/05/how-to-remove-html-tags-from-string-in-c/
JavaScript code
http://mscrm4ever.blogspot.com/2008/08/stripping-html-tags-from-email.html
A sample plugin
http://blogs.msdn.com/ukcrm/archive/2008/07/10/converting-html-e-mail-to-plain-text.aspx
Bye..