adding www to the url

Create a subdomain www.domain.com that links to the same as the main domain.

can you please explain it more

I assume that you are hiring your domain from some provider, right?
If so, go to their site, login, and search for "subdomains" in a control panel of some sort.
Then add the subdomain www.domain.com and make that link to the same ip/port as http://domain.com

Ah, I think i am mistaken... you can acces http://www.domain.com/ right? But you want  http://domain.com to be http://www.domain.com, if so:

Options -Indexes +FollowSymLinks

place this .htacces file in your root directory:

RewriteEngine On
RewriteBase /
RewriteCond %{HTTP_HOST} ^domain.com [NC]
RewriteRule ^(.*)$ http://www.domain.com$1 [L,R=301]

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Hi

You need to rewrite url from non www to www.
Please check article
http://track.nextmill.net/KB/a85/rewriting-non-www-to-www-url-iis7-servers-only.aspx

This explain how to achieve this in IIS 7 using .NET

Hope this will help you

http://weblogs.asp.net/zroiy/archive/2008/08/17/missing-windows-authentication-provider-for-iis-7-on-windows-server-2008.aspx