athena, Riverview will download into 'your name > Documents > Electronic Arts > The Sims 3 > InstalledWorlds' as will Barnacle Bay if you purchase that town. You can do the same for that folder - just transfer to your thumb/flash drive and then transfer to the same folder on your home computer.
If you purchase any items they too will be found in the Downloads folder.
My 9 year old granddaughter just has The Sims 3 CAS and she is always sending me Sims and clothing she has 'designed'. I, in turn, download patterns and Sims 3 clothing to my game, copy them to a thumb/flash drive and send them to her. She is too young to play the game and they have no internet where she lives but she is happy helping me 'play'. We look forward to our exchanges each month.
Good Luck and have fun!