It seems to be a common problem and here’s a fairly easy solution.
- Build the adhoc version of your app.
- Drag your build (.app file) into iTunes and sync.
- Go to your iTunes Mobile Applications dir (e.g., /Users/bear/Music/iTunes/Mobile Applications)
- Find your app’s .ipa file (e.g, NoonView.ipa)
- Email that to your Windows-bound friends (along w/ the adhoc provisioning profile).