I work on a portal product which incorporates SSO features. Faced with the requirement to allow SSO into Web applications requiring Windows Integrated Authentication (e.g. OWA using NTLM), I discovered Microsoft support KB article 836640 (http://support.microsoft.com/kb/836640). This solution appears to work perfectly for many OS/IE combinations, but fails using Windows 7 with IE8. Using the example code (page) given in article 836640, I am always presented with a login dialog, forcing the user to input their username and password. Looking further into this problem, I found KB article 823659 (http://support.microsoft.com/default.aspx/kb/823659). From section 10 of that article (Network security: Lan Manager authentication level ), I tried the various different options that seemed relevant but nothing resolved the problem. Any insights would be greatly appreciated. I noticed that the former article, 836640, was last reviewed about two years ago - if it were updated to reflect the situation with Windows 7 I'm sure it would be of immense value.