Even though IE7 was available in beta for webmasters to test compatibility with their website, many have either not attempted changes or attempted updates for IE7 compatibility. As a result, there are websites that will not render correctly when accessed with IE7.
In order to solve that problem, Microsoft released the "User Agent String Utility" not long ago and recently updated it to Version 2. With User Agent String Utility, Version 2, an Internet Explorer 7.0 window will be opened that is configured to report its identity to websites as being Internet Explorer 6.0, thus allowing the full security measures afforded by IE7, yet the ability to access sites that have yet to be updated.
User Agent String Utility, Version 2 is available from the Microsoft Download Center. Note that Windows Genuine Advantage validation is required to download the User Agent String Utility.
Supported operating systems include Windows Server 2003; Windows Server 2003 Service Pack 1; Windows Vista; Windows XP; Windows XP 64-bit; Windows XP Service Pack 1; Windows XP Service Pack 2.
Additional information is available in the IEBlog.