I created an adhoc version of my app (.ipa) and I sent it to a my friend; now he hasn't his mac, can he install .ipa without macbook (with iTunes) on his iPad? or .ipa is possible to install only through iTunes with a mac?
If you are interested in OTA installs, I would check out TestFlight, they are free and honestly fantastic.
Your friend can install the app using iTunes on Windows, but you will still need to make sure his UDID is added to the provisioning profile you built the app under. Otherwise it will fail on his end for code signing issues. TestFlight is good for making sure these are resolved before publishing. Otherwise you can put the .ipa file on dropbox for your friend to download.