In most our themes we use Hupso script to implement social networks share functionalities. In a similar way you can place any code. Here is the guide:

1 On site http://www.hupso.com/share/ get code and put it to CMS->Static Block. footer_links Put it inside this div

<div class="share_this"></div>

2 On site http://www.sharethis.com/ get publisher id and place it here System > Configuration > Design > HTML Head.

Edit field Miscellaneous Scripts

Place your publisher id instead of the one which is in there