Microsoft has released Windows XP to manufacturing and made Internet Explorer (IE) 6.0, a key component of XP, available for immediate download. However, a key difference exists between IE 6.0 for XP and IE 6.0 for Windows 2000, and it affects Outlook users. If you click File, Send, Link by E-mail to send a link to a Web page from IE 6.0 on an XP machine, the browser inserts only a .url file--it doesn't insert a text link in the body of the message. Because the Outlook Email Security Update blocks .url files, users with that update will receive a message that contains no usable link. IE 6.0 on Win2K, however, inserts both a .url file and a text link.
http://www.microsoft.com/windows/ie/