I'm trying to provide read/write access via WebDav to a webapp of mine,
which generates Excel output of some tabular data. The idea is that the
user, from an ordinary web page, downloads an Excel file, edits it and
can then save it back.

Now this works well enough if the URL is typed in directly from Excel,
e.g. I can specify http://server/file.xls (which really is dynamically
generated) which Excel fetches & saves using WebDav's GET / OPTIONS /
PUT / PROPFIND.

However, if that file is linked to from within IE, it is read-only; I
can only "Save As" to the local disk. This is regardless of wheteher
XLS files are configured to open within the IE window, or in a separate
window.

One last refuge I have is to allow my web app to display a "Web Folder"
with the file, where the file would be editable, this can be done
semi-automatically through a "davhole" approach by displaying it in an
IFRAME, but it is kind of ugly. I'd really like to link directly to the
file, prompting the user for download but then after download, make it
writable.

Any clues?