The Social Float plugin displays facebook,twitter, buzz and digg buttons for your viewes on a floating bar, like mashable and cracked.com.
The plugin defaults to your single.php file. Some themes may require you to hard code the function call into your template. Please visit http://seocampaign.org/word-press-plugins/updated-social-float-plugin/ for instructions.
Go to the plugin settings and change the conditional tags to get the bar on your required page/post. See http://codex.wordpress.org/Conditional_Tags for more info on conditional tags.