It is indead possible (I have done it). If you model on GENERIC.C from
the Excel 97 SDK CD, the last argument in the g_rgWorksheetFuncs array
is the help string for the first argument (which gets reused for
subsequent arguments if no other help strings are registered). If you
supply additional arguments (some adjustment of demensions and loop
limits required), they will be interpreted as help strings for
additional arguments.

Jerry

Tom Ogilvy wrote:

Jerry told you how to do it for VBA UDF's. I believe you can in an XLL
although I have never built one, but Laurent Longre implies that it is
possible to do it directly in an XLL. XLL construction is covered in the
Excel Software Developer's kit, but that has been discontinued back around
xl97 I believe (or perhaps earlier). I believe the documentation is on
MSDN.