IIRC you need to specifically tell Installshield to include support for 64bit OSs.

Does the Installer just fail with a not supported OS message or does it crash or what specifically happens?

>>Has anyone experienced problems installing and running a compiled VFP app into a winXP64 or winMediaCenter PC?
>>
>>I have a app that my user says will not install on either of these systems but it works fine otherwise.
>
>You should test application on all Windows versions you expect it to run on before releasing it.