I have neen doing it for several years now. I have seen three methods:
1 - MSCOMM
2 - Common Basic statements of OPEN, PRINT/WRITE, CLOSE and
3 - The method I use, API calls into the Kernel32.

I am using Excel 97 and it will not run MSCOMM. Something about not
being licenced or approved. I don't recall the exact wording of the
message I got when trying to load the MSCOMM module.

I can send you workbooks that have methods 2 & 3. I have seen MSCOMM
examples on the web as well. They may be large !! 3-4 meg. They
send out the serial  port to operate ham radios and are quite envolved,
but you should be able to use the module.

My method has one module with very good comments and was written by
someone who knew what he was doing.