I saw it from Message 622328 of Nadya Nosonovsky (USA)and It it works very well.

This goes in the program that launch your application:

=myInstance('smvfp.exe')
&& maybe the first line

then, place this code at the bottom of the launch application:
*********************
Procedure myInstance
Parameter myApp
=Ddesetoption("SAFETY",.F.)
ichannel=Ddeinitiate(myApp,"ZOOM")
if ichannel =>0
wait window 'Yourprogram is already running. This will finish' timeout 5
Ddeterminate(ichannel)
quit
endif
=Ddesetservice(myApp,"define")
=Ddesetservice(myApp,"execute")
=Ddesettopic(myApp,"ddezoom")
return
*******
Procedure ddezoom
Parameter ichannel,saction,sitem,sdata,sformat,istatus
Zoom window screen Norm
return
*********

This code works for VFP6 and VFP7.