Download it here: http://www.apple.com/icloud/setup/pc.html
Important Updates for Windows Users :-
Shared Photo Stream support
The ability to create or respond to shared calendar invitations directly in Outlook
Improved event invitation behavior
Built-in calendar notifications
Improved...
Here it comes :-
iCloud unveiled at WWDC -- Engadget
Few more updates :-
-->Apple adds camera shortcut to lock screen, volume up shutter key, and other enhancements to iOS 5
-->Apple unveils iMessage, its BBM competitor, at WWDC
Source : Engadget !