If you have an Apple ID and you have already inserted it in your Apple TV, you already have iCloud.
You can use Photo Stream without a iOS device. First, install iCloud Control Panel in the PC.
Then, iCloud Control Panel will be installed in Control Panel, so open Control Panel > Network & Internet > iCloud, log in with your Apple ID and mark Photo Stream. Next to Photo Stream, you will see an Options button, so press it and you will see where the Photo Stream folders are.
You just have to put the photos you want to use in Photo Stream into the download folder, so they will appear in the Apple TV