Windows apps can talk to iCloud according to this page http://developer.apple.com/icloud/index.php

"read about the new iCloud Storage APIs in iOS 5 and OS X Lion to learn how you can incorporate iCloud into your apps."

"You must have a Mac running OS X Lion 10.7.2 or a device running iOS 5 to utilize the iCloud Storage API for Documents."

I don't see any mention of Windows

I saw the word "Windows" on this page http://developer.apple.com/icloud/index.php and jumped to conclusions. My bad.