> The obvious thing to do is to tap into the xtal output.
> So, can somebody tell me what sort of electronic wizardry I have
> to do to make the 4MHtz crystal drive some sort of gate so I can
> divide by 4 and drive the ISD chip???


Careful.

Check the spec, there should be an output drive spec for that pin. If not,
you're in shaky territory, no matter how many hobby projects or protos "just
worked".  The most interesting part of a data sheet is often what is NOT in
it.

I had a similar case, where I disapproved of this arraingement because there
was no output drive spec, and the eng mgr told me that all the protos
worked, and "don't worry.."   Guess who got to fly to kaohsiung christmas
day to debug an assembly line full of product that didn't run... :(

Startup time on the osc may be affected too, but only you can answer if that
matters to this application.

In many cases, that output is designed to only drive a crystal.

Also, remember to check the effect of that gate capacitance on the osc
circuit.