Looking at the user agent we get information about the visitors, such as
the operating systems they are running, browsers they are using, or
what version of .NET Framework they have installed. The user agent is
retrieved differently depending on the programming language you are
using for your website.

Since Internet Explorer 6.0 is the dominant browser, the most
common user agent string are similar to:

Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1; .NET CLR 1.1.4322)

MSIE 6.0 is what tells us the name and version of the browser (Microsoft Internet Explorer 6.0).

Getting back to the topic of the question, Microsoft Internet Explorer 7.0 Beta 1 can be recognized by MSIE 7.0b, such as in the following user agent string:

Mozilla/4.0 (compatible; MSIE 7.0b; Windows NT 5.1; MathPlayer 2.0; .NET CLR 1.1.4322; .NET CLR 1.0.3705; .NET CLR 2.0.50215)

The final release of Microsoft Internet Explorer 7.0 will be recognized by MSIE 7.0 inside the user agent string.

If you see an user agent string similar to the following, it means the visitor is running Windows Vista and browsing the web using Internet Explorer 7.0 Beta 1:

Mozilla/4.0 (compatible; MSIE 7.0b; Windows NT 6.0; .NET CLR 2.0.50215)

For more information about getting operating system information, please see How to detect if the visitor of a website is running Windows Vista.