I have a SharePoint 2007 site on Windows Server 2003 R2 that is set up to require SSL/HTTPS and client certificates on the IIs Web App.
Opening Document Libraries in Windows Explorer works fine from Windows XP IE6 clients. However, from Windows 7 (64bit) IE8 I get this generic, well known, error:
Your client does not support opening this list with Windows Explorer.
Turning off the client certificiate requirement (but still requiring SSL/HTTP) makes it work, so it's not really related to SSL/HTTPS nor is it something fundamental missing in regards of WebDav support. However, I do need client certificates.