Just a word of warning – if you need to check for a specific version of Internet Explorer, do not rely on JavaScript. While working on a project where I was applying JavaScript to customize a closed-source package (yes, we were allowed to do this by the provider), we wanted to make sure that users were using only IE8 and up.
Fairly simple, right?
Well, no. It seems the package we were using was putting IE9 into quirks mode, which (much to my surprise) causes the user agent string to report the browser as IE7.
So, no JavaScript to detect the browser version.
On the server-side, the user agent was coming through correctly, so at least we had a different avenue on which we could proceed, but it seems rather peculiar that there would be no way to correctly identify a browser because of how it is rendering the page.