You should upgrade squid to a current version and add :
acl WEBDAV method PROPFIND TRACE PURGE PROPPATCH MKCOL COPY MOVE LOCK
UNLOCK DELETE PUT GET HEAD
(Maybe you want to limit the available command set)
With this acl you can then construct a http_access line that allows
access to WebDAV services to a subset or all of your clients.
You will find the current squid useful in other aspects, too : delay
pools and other nice features.
You can install the new squid on the same machine using a separate
configuration file where you define a different port and cache_dir. In
this way you can safely play around with the new one and move it into
production when it is stable (hint : this will ork only when you do
_not_ install squid into the same location as the old one...)
Hope this helps,
Jakob Curdes