You need a iPod touch 3rd gen, 4th gen ( including current ones ) with iOS5 to be able to sign for free up to iCloud, get the @mac.com adress and the 5GB of backupspace for the iPods content, calendar / adressbook and Mail syncing. Your purchases of Apps,Books and Music are backed up by Apple and don't count against your 5GB.
To use "Documents in the Cloud" you need to buy pages,numbers,keynote for iOS5 on the iPod.
On a Mac you need OSX Lion, version 10.7.2. You also need iTunes 10.5. For Photostreams you need iPhoto9.2 . Optional iwork09 v9.1 or Microsoft Office to use your mobile iWork documents on the Mac.
On a PC you need Vista or Win7 and Outlook 2007 or 2010 plus the free iCloud controlpanel plus iTunes 10.5. You would need a Office Suite like Microsoft Office 2007 or 2010 to open the iOS iwork's documents that are stored in www.icloud.com.
So you have some options. A Desktop Machine is not needed. iOS5 devices can live on their own, they are "PC-free", independant devices on their own. In conjunction with a iCloud capable Desktop or Laptop you get the most out of it but also if you own more then one iOS5 device ( say 2 ipods or ipod and ipad ).
Message was edited by: Sjazbec