1. IE6 users on Windows 2000 cannot upgrade to IE7 and will not be forced to do so.

2. IE6 users on Windows XP/2003 will be forced to install IE7 only if they blindly allow the MS update mechanism to install any junk chosen by Microsoft, no questions asked. So IE6 on XP is still possible, although there might be no more security updates offered for it.

3. Windows Vista users never had the option to run IE versions older than IE7.

P.S.
The safe way to handle gzip or deflate compression (the latter should be better than gzip but has more browser bugs) is to let the web server do this based on the headers in the request (”Accept-Encoding” and “User-Agent”). As someone mentioned, the Apache web server standard example configuration does this out of the box. For IIS and other web servers, configuration scripts may be available somewhere.