>I used IS 3, that comes with VFP 8, to build a Setup. In it's project I choose to install on Specific OS (Only Win95 is forbiden), but when the user try to install on Win 2003 Server an Message appears "The operating system is not adequate for running [My Application Name].

Is Win2K3 server on the list? If it's not, you'll have to allow install on all or use ISX 5 that comes with VFP9 and has checkbox for Win2K3.