How to send a net.mail body as Web.mail body?

Hai,
          In asp i tryed to send mail with images. so i  used AlternateViews and  LinkedResources from System.net.mail class.
before sending the mail i would like to add
email.Fields.Add("http://schemas.microsoft.com/cdo/configuration/sendusername", username);
here System.net.mail class doesn't contain Fields. System.web.mail only have Fields.
is there any a;ternative for this problem. hepl me .

...