Anyone with 'Edit' rights can edit the attachments. You can verify this at
http://91.121.237.216/xwiki/bin/view/WebDAV/ by registering a new account
and trying to edit one of the attachments. If you still can't edit the
attachments there, that means there is a problem specific to vista. Can you
verify this ?
PS : server at 91.121.237.216 might not be available all the time because
it's a *test* server ;)
Thanks.
- Asiri