What a great resource Universal Thread is. I'm moved by the willingness of people to help. I learned something from each of the responses.

I settled on Bob Lee's suggestion. I downloaded the sh_execute function and put it in my standard procedures directory along with ShellTo.prg:

parameter pFile
set classlib to sh_execute addi
ex=create('sh_execute')
ex.shellexecute(pFile)

Now I can open any file with :
=ShellTo(m.filename)

I love it. Thanks guys.

Martin