From PinataIsland.info, the Viva Piñata wiki
Xbox Live is a subscription-based online gaming service for Microsoft's Xbox and Xbox 360 video game consoles. There are two tiers of service: Silver and Gold. Xbox Live Silver is free, and allows you to download extra game content, demos, gamer pictures, patches and more. Xbox Live Gold requires the payment of a subscription fee -- US $49.99 per year (approximately £39.99 per year) -- and enables users to play online games against each other. Also some content such as demos has, more recently, been released to Gold subscribers first and then to Silver users some time later.
In Viva Piñata, it is possible for Xbox Live Silver or Gold gamers to exchange and send Pinatas online as presents, to and from another player's gardens. You can then interact with that person's Piñata. The Piñata will feature a tag that contains all the individual and unique data about who it is and where it’s from. This is enhanced by the ability to customise any of your Piñatas with accessories which can be acquired from the Xbox Live Marketplace. Like a lot of Xbox 360 downloadable content (DLC), these items must be purchased with Xbox Live points, which are in turn purchased with real money.
Basically anything you see in the game can be packed up into a crate and shipped over Xbox Live to anyone on your friends list. (The friend that you are trading with must play Viva Piñata on the same gaming platform as you. It is not possible to ship Piñatas between Xbox Live and Games for Windows gardens.)
Via the Xbox Live online community, players can contact other Xbox Live Silver or Gold gamers to trade items, however, there is no option to visit the gardens of other players, or invite vistors to yours.