Digest authentication and freezing in IE

I have set up an IIS6.0 website to use Advanced Digest authentication. It
works fine for normal page views. It does not work for an application that
is left open for a long time:
- it prompts the user to re-authenticate every x minutes
- if the user ignores it, IE6 freezes at the prompt and won't respond. It
needs to be terminated in Task Manager
I can see in the Digest RFC there is a provision for renewing the
authentication periodically. It says that the server _may_ allow it to be
renewed without prompting, or it may request a new authentication. Two
questions then:
1) Is IIS supposed to prompt the user to re-authenticate every x minutes?
2) Does IE6 freeze if the prompt is not responded to?
Thanks,
Anthony