I've followed some of the recommendations by Nolan on other 'ad hoc' questions in this forum.
I have reached undiscovered territory it seems.
When I send the .app file along with my .mobileprovision file to my client they can import the .mobileprovision, but the .app is a different story.
THe .app on a Windows machine is a folder. iTunes can't import the file because it sees it as a folder.
How do I deliver the necessary files in the proper format for a Windows installation using Ad Hoc?
I've tried changing the .app to .ipa.
If the above doesn't work for you, just open your iTunes, select the app followed by "show in Finder" and finally send that .ipa to the client.
Works for me every time.
When I send the .ipa it will show up in iTunes without an issue, but when the client syncs an alert shows up saying that the app is not signed. I've sent them every .mobileprovision profile that I have.
Clint Tredway answered this. He helped me offline.