replication using a filter driver

Hi all,
I’m a newbie to NT kernel programming and I was looking to explore a way to
provide a replication filter driver. I can attach my filter to any number of
file system drivers, but how do I forward create and write requests to two
target devices when I trap it for one of them ? Can I simply duplicate the
code for forwarding to the device object on which I’m stacked , i.e. forward
the IRPs ? Will ths work for the “other” device object to whom this request
was not directed ?
Also, how would I communicate between this filter and a user level process ?
E.g. if I want a pop-up in Explorer whenever a user accesses a replicated
folder, can I communicate this to some user-level daemon of mine running in
the background, which can then launch a message box ?