Wanted: AutoLISP routine to snap line vertices to nearest point on apolyline

Hi,

I am looking for an AutoLISP routine for use in AutoCAD 2007. The
routine needs to:

-- Look through an entire drawing, including inside of block
definitions
-- Find all lines on a given layer
-- Move (snap) the vertices of said line to the nearest vertex of a
polyline on a different layer

So, basically, said routine needs to go through an entire drawing,
including looking inside block definitions... find all lines on a
layer of a given name, say "GUIDE_LINES"... snap the vertices of
these lines to the nearest vertex of a polyline on a different layer,
say "MAIN_SHAPE".

Basically, the reasoning behind this is that we have some external
software that we need to feed the resulting DXF... said software needs
to have the points of our "GUIDE_LINES" layer matched exactly to
points of the polyline shapes on our "MAIN_SHAPE" layer (those aren't
the final layer names, but just for example).

Hope this makes sense. Would be willing to purchase a pre-existing
tool or pay a sensible fee to anyone willing to provide such a script.

Pretty urgent, so would appreciate any responses.

Many thanks in advance!

Andy