iCloud is not something that you download
it is a service.
Get yourself a MobileMe account, they're free, log into it via the System Preferences pane and you are good to go.
When you get home, do the same for the iMac and you are set
To create a free iCloud account, you must have either an iPhone, iPad, or iPod touch with iOS 5 or a Mac with OS X Lion 10.7.2.
That answers the Lion download question for the iMac, does your iPad/iPhone both have iOS5?