For some reason you need to produce different output depending on the HTTP client being used to view your site.
The guess_browser_version() method of the HTTPRequest class returns the name and version of the HTTP client.
browser, version = request.guess_browser_version() if browser == "MSIE": return msie_page(request) elif browser == "Mozilla": return mozilla_page(request) else: return default_page(request)
Alternatively, you can examine the User-Agent header and pick it apart with regular expressions. However, the header values are usually confusing -- every browser claims to be Mozilla, for example -- so you're likely to spend some time getting your regex patterns just right.
Do *not* assume that all users are using either Internet Explorer or Netscape/Mozilla, and deny access if the browser isn't one of those two. This is highly irritating to users of Konqueror, Opera, Safari, and it's easily avoidable by writing your application properly.